i dont think the screen looks that bad, sure the leaves look crap, but the rest is fine. i would have a hard time believing that valve would choose the release a image not at full detail. maybe they are just saving the best till E3. u can pick any great game and find crap textures/models, its...
they dont even ship the CD's, they just send a master to each country for pressing. there is no excuse why some countries should get it later, other than the US wanting to have everything first.
once the cpu can do the AI, and other CPU dependent features, u only need slight increases to keep up with the gfx card. hl2 will be limited by gfx cards so the sound isnt an issue with the fast processors that are around.