I used MGS as an example based on a time frame. The xbox also only had a what, a 3.5-4 year shelf life before its next system. So if, like you said
All it was was a console stuffed with off the shelf pc parts. So, it was pretty much tapped out on day one. Shouldnt the PS2, being the pain that it was, have some leeway?
Halo
Release Date: Nov 14, 2001
Halo 2
Release Date: Nov 9, 2004
MGS 2
Release Date: Nov 12, 2001
MGS 3
Release Date: Nov 17, 2004
Now do you see why I used the MGS's as an example for the PS2?
If that is not good enough try this one.
SSX Release Date: Oct 30, 2000

SSX On Tour Release Date: Oct 11, 2005

Like I have said, there is a difference, but it is not that big.
I understand why you used mgs as a reference point, as time frame goes, but it was not a first gen game; the devs were resonably familiar with the ps2 hardware by then, whereas halo 1 was first gen for the xbox.
If by leeway, you mean that current ps2 games should look significantly better then its first gen games, then yes, it should. Compared to xbox current games vs. its 1st gen games, the ps2 improvments is much greater.
Also, not only does screenshots not give a good rep of a games overall picture quality, but EA is one of the least of all devs that push any hardware, performance wise.
I find it also hard to believe that consoles will ever surpass what the pc has to offer graphically. They may be equal for some time, put the pc always pulls ahead adventually. But i still believe, due to the multi-core structure of the next gen systems, that the games visual improvents will increase much more as time goes on then the previous last gen systems.