Sorry for double-posting, what follows is just so... "out of template". Read this if you're interested in further details or take it as a testament to the effort I put into this particular DR :P
Like probably some other recent cross-platform titles, Pure has a tricky way to deal with aspect ratios : 3D and FMV look best in 16:9, while the ubiquitous stretched 2D elements make the game look "not quite right". The design of most 2D elements is pretty clever too, and it often requires a sharp eye to find out which aspect ratio is "correct" for each element of a picture on screen. I think the makers of Pure realized that although 16:9 is the natural aspect ratio for 'next-gen' consoles versions and their HD resolutions, it was much less common than 4:3 on the PC. So they probably re-designed 2D elements to make sure they wouldn't look too weird in 4:3, while the game itself and video files remain 'HD'. Here are more comparison screenies to hopefully demonstrate this better than my clunky words.
ATV selection screen : 3D Hor+/2D stretch. Then again, the coloured bolts on the 'stat screws' look better in widescreen than in 4:3 to me.
Track selection screen : seems to stretch... but only the upper-layer 2D elements (world map, 'Freestyle' circle...) do ! The bink video file looks exactly the same as the background of the 1360x768 shot. The mountains, clouds and trees are too narrow in 4:3, even though the photo's white frame seems to have more "familiar" proportions than in widescreen.
Loading screens : you'll come across a lot of these in Pure - before as well as after races. And you'll see loads of those rotating gears that look like potatoes in widescreen...
Garage : although the background video (moving black lines and arabesques) is really another 16:9 FMV, this screen would make you think 4:3 is the real aspect ratio intended for the game... Then you'd do some racing and realize it can't be. 2D's a liar in Pure !