the problem probably is...
It seems like Diablo 2 runs in intel macs through Rosetta, an emulation piece of software that which is "the greatest software you'll never see", as apple advertises it.
That's basically why it runs so badly in mac, and we don't have any new OSX features for it. It's not that the game is ported and done by blizzard to work in Intel Macs, it's just using a generic Apple tool to do it.
So, in a nut shell, just give up and get to play new games already or stick with all those minor issues, since the game does run fine enough! 😛