You're right, it is because the specs are fixed. But you're also wrong, PC gaming will have nothing on consoles come next generation.
The PS3 is just the start. Games that come in the next two years will simply not be possible on PCs.

As a programmer, a computer engineer, and someone who does this for a living, I'll try to put some explination into this.

1. When you develop for a PC you have to deal with the operating system taking an overhead of the system resources. With consoles this is very little on the ps3, and more on the 360 (And I've used both dev kits to prove this.)

Besides that, every single aspect of the code and engine is designed to work specifically with the hardware that is in the system. This is why multi-plats (generally) look worse than exclusive counterparts. When you see a game that does not look as good on one console compared to the other, it is simply because the developers did not put enough work into the engine for the console which is inferior.

2. This is why I hate comparison videos and such. Developers have become lazy, and it takes people like rocksteady to make things right. Anyway..

3. Games like Metal Gear Solid 4 are simply not possible in a multi-platform form. People seriously underestimate just how good metal gear solid 4 looks. I know that because of the nature of the game a lot of it doesn't always shine, but the character models, animations, guns, effects, and even most of the environments in this game are done better than crysis, far better than crysis actually. MGS4 was bar none the best looking videogame ever made when it came out, and until we get heavy rain or gow III, it still is. It may have low textures in some parts, but that is simply due to the complete overkill that was done in other parts of the game.

4. Mind you, MGS4 was incredibly expensive, as well be gow III and heavy rain. You simply cannot get that kind of technology without intense optimization and research into the hardware. This is why games like Alan Wake, which does look absolutely amazing, will not look as good as MGS4/HR. Its nothing to do with the hardware, it's to do with the money invested by the developers. Remedy is far from rich...

5. You could make Heavy Rain for the PC right now, but it would require hardware that doesn't exist, unless it was designed for specific hardware, which would be useless for a PC. it needs to work on all sorts of hardware.

So to close off the OPs statement, you're absolutely right. As consoles progress and developers get better, it's going to become harder and harder for PC games to outdo games that are designed for specific hardware, the few games I've worked on are all multi-plat titles and we always use one engine. It's very hard to optimize the engine for just TWO sets of hardware, imagine doing it for the pc? would be sick

You're talking to a fellow programmer btw (Reasonable)

1. Theres a sheer brute force difference which cannot be overcome. The HD 58xx range from AMD is 2Tflops+ and the graphics cards have tricks up their sleeves that the PS3 couldn't hope to compete with. Shader model 5 vs shader model 3 for instance, tessellation, multi-threaded rendering, compute shaders etc.

2. Say that to their face why don't you. Actually stand at the door at crunch time and call them lazy, I wanna place bets to see if it would provoke anyone to take a swing at you. (no offense intended)

3. Funny the times when the game really shines are the times when you can put down the controller and watch... funny huh?

4. Expensive yeah... but doesn't look as good as a game which cost half as much to make (Crysis), which I might add was released in 2007.

5. Hardware that doesn't exist huh? You'd probably nail that sucker out at 2560 by 1600 with an AA mode of your choosing and 16x AF on a modern GPU at the same frame rate as the PS3. Its a visual intensive game, theres very little else to it. What good that the Cell brings is being used to make it look pretty and a PC with say an HD 4870 or better under the hood doesn't need to call on the CPU for help.

Again, you could do it, I never said you could not. I simply said development would be very difficult because you would need to ensure it would run on a wide range of hardware. Of course Brute force will do it, but what happens next gen? We get even closer..

Think about it? Why hasn't their been any PC games to come out over the last 2 years that rival the console exclusives in terms of graphics? What if the next consoles have cards that are as good as 4870s(4890 is where its at imo..)?

WIth PCs you're forced to develop for ever changing technology, its really difficult to optimize on them. In general, you do very little optimization.. CRYTEK is actually amazing at optimization, and look how well that went?  Basically no one could play the game when it came out.

CRYTEK has developed the cryengine 3 for consoles and PC. While the PC does look better, they have invested a lot of time and resources into making the consol engines and they look just about as good. If this isn't proof I don't know what is.

You're talking to a fellow programmer btw (Reasonable)

1. Theres a sheer brute force difference which cannot be overcome. The HD 58xx range from AMD is 2Tflops+ and the graphics cards have tricks up their sleeves that the PS3 couldn't hope to compete with. Shader model 5 vs shader model 3 for instance, tessellation, multi-threaded rendering, compute shaders etc.

2. Say that to their face why don't you. Actually stand at the door at crunch time and call them lazy, I wanna place bets to see if it would provoke anyone to take a swing at you. (no offense intended)

3. Funny the times when the game really shines are the times when you can put down the controller and watch... funny huh?

4. Expensive yeah... but doesn't look as good as a game which cost half as much to make (Crysis), which I might add was released in 2007.

5. Hardware that doesn't exist huh? You'd probably nail that sucker out at 2560 by 1600 with an AA mode of your choosing and 16x AF on a modern GPU at the same frame rate as the PS3. Its a visual intensive game, theres very little else to it. What good that the Cell brings is being used to make it look pretty and a PC with say an HD 4870 or better under the hood doesn't need to call on the CPU for help.