Like I said, people won't see a difference as long as you keep putting the whole picture.
Most people don't have a 40+" display with a 1920x1080 size (and running at that size) to see the difference.
You would have to take 1/4th an image that size (and doing the same with the 640x480 one) so that everyone can see the difference.
Even then, it's not sure they see the difference, it won't make a lot of sense.
You basically can't compare HD vs SD on a monitor at home. Especially since every display technology have their problems. For example, LCD have ugly screendoor effects and the worst black levels, among other things.
The fact is that Home Theater world is plagued with BS from everywhere. Few people understand what the settings are for, as they don't even always have the same meaning among manufacturers (like contrast).
The KDS from Sony are the best displays at these levels of price, blowing away most plasmas and every LCD, but that's once it's well set (actually, it destroys all LCD even when not well set). The default settings are ugly, but apparently, they do that because that's what people want (but they want that for no more that 10 minutes, they eyes and their brain won't stand it for long).
The chip on this SXRD display is so good, that it's better than most DVD upscaling players out there, that will do a far poorer job upscaling and deinterlacing DVDs.
LCD sell like hot cakes, but they are the poorest quality of HD displays. There are lots of talk of 1080p, but no content comes at 1080p, except for games, and I'm not even sure of that. I'm talking the source there, not what's out of your HDMI cable. A lot of people don't see a difference between 720p and 1080i because of all this nonsense. And they're right, there's no difference, the 1080i should even be worse, given our compression algorithms.
People that play games buy plasmas (!!!). It's actually as much a nonsense as the rest. But yes, the plasma will be burned by the games, that's the worst display to buy to play games (despite being one of the best quality), unless you can afford to buy a new one regularly.
In stores, you often see HD displays that don't even are at the right ratio !!
When I started getting interested in HD, I couldn't understand one thing of it, and yet, I'm used to complicated stuff. Now that I know more, I understand why : this is a big mess, where they sell lots of nonsense to people, that don't understand any of it. People think the image is better, just because it's really bright ! I hear that everytime !
People basically buy HD, not because of HD, but because the screen is flat. That's why you can see a rear projection TV using SXRD blowing away the quality of even most plasma TV around it, and people still buy the plasma (and LCD), for twice the price or more, to add insult to injury. But the plasma is thinner and you can put it on a wall !
That's why I don't think most people buy HD for what it's for : quality. They buy HD for other reasons, and I can't blame them, as it's worse than gaming : only people knowledgeable enough can make an informed purchase in this field, and they are a few. Displays in stores, which are nearly always badly configured by default (to blow away the passersby's eyes) unless a fan configured them, aren't even a good mean to gauge them.
I only decided that perhaps I should leave my old SD rear projection behind, when I saw this very specific display was the only one at an affordable price, that could make SD look better than on my old SD set, despite having worse black levels (but everything else is better, and it upsamples everything to 1080p).
