It's not about art or money, it's about EGO and PRIDE. How would you feel if you worked your butt off on scenes that you thought would improve your movies only for the majority of viewers to complain about how much some of the scenes suck? Would you just turn your back on what you did? I think in George Lucas's mind he had too much confidence in the changes to be improvements, I'm sure deep down in his heart he really felt the Jedi Rocks, Han shooting first, the butchering of the ROTJ end music, etc.. etc.. all were great additions.

Lucasarts could realistically create a box-set DVD with both Special Editions and the originals and it could sell for $100, it'd still sell an unbelievable amount of copies. But that would be a complete slap in the face if that box set sold nearly as well as just the Special Editions. George Lucas just doesn't want to be proved that he's wrong, it's not about art, Empire Strikes Back and Return of the Jedi aren't even his art for god's sake!