And for touring as well -- nothing like completely eliminating chain lube and cleaning equipment from your panniers. Plus, drive belts last something like 10-20k miles, so the price difference quickly pays off. Plus you don't have to worry about anything snagging on and breaking a derailleur, and belts work better in cold conditions, too.
I see them as the drivetrain equivalent of disc brakes -- sure, rim brakes are still around. But the tradeoffs are so worthwhile that you effectively can't buy a high-end bike with rim brakes any more (disclaimer: I know that certain touring bikes come with cantis by default, but they're rarer and rarer each year).
The only difference I see is that internal shifter hubs can cost 5-10% efficiency compared to derailleurs. In the commuting and touring communities, that's no big deal -- it's comparable to dynamo loss, which is considered a totally acceptable tradeoff for always-on lights in those communities.
But in the racing community, chains will probably stick around for a long time, at least until internal hubs lose that efficiency loss. There's just too much to lose in that 5-10% for racers, even if it's totally worth it for me.