Are you aware that the vast majority of PlayStation 3 and Xbox 360 games are not natively rendered in high definition, either?
I apologize if I've derailed this into a question of how easy it would be to re-do the artwork. But it should obvious that that's not required to make these games run in widescreen format on a high definition television and have them look great. Again, Sonic's Ultimate Genesis Collection is an example of a package that ported over forty titles with relatively little hassle and very nice results. I think the difficulty of SE making this happen, as stated early in this thread is greatly exaggerated.
Also, Mirage, I think it's ridiculous that you want proof of emulators that make games look better than they originally did at higher resolutions (not native HD). If you can't do this yourself, then I truly feel sorry for you, because you're missing out on a really great thing.