They are in game.
Before meeting Naomi in act 2, I crawled onto a pink carpet with my octocamo on , including the mask.
Well lets just say that Snake did not look at his best during the 10 minutes cut-scene following that, talking to Naomi while wearing a pink outfit :P

Some cutscenes are obviously in-game, but that's all you have proven.

I have seen several screenshots of cutscenes with video compression artifacts, notably the screenshots sieanr posted of a cutscene in Act 3:

Example:

Look at the square blocks there. Also, if you do right click + view image to be able to see all of it, look at the place a bit above the building. The artifacts are even more obvious there.

If you want to make up your mind about this and you have the game, check this cutscene and look at the sky. If you've seen downloaded DivX movies before, you'll probably know what kind of artifacts I'm talking about - color gradients lose in quality and number of different colors, having sharp color changes and being blocky. Then post your findings here.

They look great, so what difference does it make?

This is as bad as the resolution arguement. If it looks good, it doesn't matter.

I think people discuss it just because they're curious. Also, if some cutscenes are FMVs (which seems to be the case), those cutscenes can't be used to hype the power of the Cell PS3 hardware.

Well by shaking the controller, you can reset the octocam in the middle of a cut-scene

It is all in game - people need to accept it. Also your camo suit is the same colour you last used. pretty neat :D

Can you do that in that cutscene I was talking about?

@finalsquall: "people need to accept it" is the least convincing argument possible.

Most cutscenes I've seen use completely different octocamo suit. There are some, like the "3 days earlier" scene, where Snake is in a suit no matter what, but it doesn't really make a different if it is in-game or not if you can't tell the difference with how good it looks.

There are 4 prerendered cutscenes in MGS4 - 2 at the end of act 3 (confirmed) and 2 at the end of act 5 (unconfirmed as i havent gotten there yet, i'm at the 3rd Beast fight). There's also the FMV with the eggs, but those don't really count.

I was profoundly dissapointed by the prerendered cutscenes at the end of act 3, but, i guess that the PS3 was simply unable to provide a decent preformance. Granted, there are some pretty amazing camera cuts and an extremely large number of very detailed characters in that cutscene, but still, it is the first MGS game to ever make this compromise. In the past they always found a "way" to keep it realtime, not now sadly.

Just play the last boss battle and start talking than if the graphics on the cutscenes aren't realtime :D