I think the main problem with laptops not running newer stuff is on-board graphics that don't support 2.0 pixel shaders for the 3D. This is the case with even very new laptops (such my month-old Hewlett Packard Pavillion for example - it has Vista Home Prof edition as the OS), it runs SH3 with GWX just fine (mind you, it does have 2 gig of RAM, which is kind of unusual for most laptops), but things like SH4 and ARMA are a no go.
It's definitely the 3D that is the issue here, as you can start a mission in SH4 on my laptop, but the moment you go to an external view or the bridge etc, it bombs out.
Not really a big deal for me, as I bought it for my job as a back up to train people on Photoshop and for the occasional blast on things when on a long train journey.
The really ironic thing with my laptop however, is that it runs the SH4 Intro movie as smooth as glass, whereas that movie is not quite so smooth on my desktop PC, which runs the game absolutely fine on full settings at 1320x1024 resolution with no hassle whatsoever - go figure
One thing my laptop does run well however, which was something of a surprise to me, is MS Flight Simulator 10, which is a notorious crippler for even high-end graphics cards.