Is that because darwine is an emulator? Will it get better when Mac becomes x86?
Can't rightly answer that question. But it is obvious that there has been a lot more work done on the wine project than on the darwine project. And there are a lot more wine users than darwine users too. Microsoft's supposedly very good VirtualPC program for the Mac makes darwine somewhat superfluous to most Mac users.
Switching data from little-endian to big-endian has to suck, especially if it is done on the fly. I don't know shit about how wine/darwine work, but I would guess that converting a Windows program to big-endian and then emulating it would be easier. Then, you could (illegally) distribute the big-endian version, so no one else has to go through the conversion process.
But that raises an even more interesting question, which no one has touched yet. Are Mactels going to be big-endian or little-endian? There's nothing that requires all Intel processors to be little-endian, they just are. Perhaps one of Apple's security strategies is to remain big-endian. Then you couldn't install Windows on a Mac, or install OSX on a PC without some serious work.