I dont get it you would think running a game like HL2 on Low Res (1024x768) with High Res textures would be better in performance than running with High Res (1280X1024) and High Res textures. But no. I can not see any performance increase or decrease either way. For example: Shouldnt One High Resolution texture cover more of a wall in a game running at Low Resolutions then a High Resolution game where the texture would need to be applied twice on the wall because there are more pixels that make up the wall?
So what gives?
Games such as HL2 makes the textures fit on the wall. However I do agree with you.
They should be releasing an upate for it soon that improves the texture quality for high end cards (ATI mainly)