There's the rub, Fritz. They're 'quasi-standard'.... the Android standard wallpaper res is 640x480.
but check it out
was playing with this last night
they've got some really cool wallpapers at interfacelift_com, but they don't come in 640x480
bummer
but if you look at the ratio - that's the same as 1600x1200
so, just as an experiment, i uploaded one of those hi-res pics to my SDcard to see if it would appear in the phone, and appear as option for a wallpaper on my home screen, and actually WORK as a wallpaper
YES!
so, you're not "stuck" at 640x480
now, those hi-res files are necessarily larger
and who wants to waste precious space on their SDcard right?
MS puts out a powertool called
Image Resizer - i have had this on my computer for a long time
one of their stock resolutions is "small" which is (tada!) 640x480! sweet!
so next i experimented with the large version and the smaller version - can i see a difference??
and the answer is "no!"
so there you have it - you can d/l hi-rez/hi-quality pics to your PC, resize them down to android size (while saving space) and not have a negative impact on the image quality - they look great!