Honestly, aside from extra storage space, why does anyone need alts, and why do all those alts need a house? We can play EVERY job on a single character: every combat class, every crafter, every gatherer.
And ckc22 is right. I was swapping decorating ideas with someone a few weeks ago who owns five houses. He was looking for ideas because he's got so many houses, he was running out of ideas for how to decorate them. If they were locked to accounts, that'd be four more people that could have a house, not to mention how many other people are sitting on alt houses. It wouldn't guarantee everyone a shot at a house, but it's better than nothing.