I have 250 gb on my desktop and that's pretty much all my storage.
While applications do increase in size over time, I find that most people are just compulsive digital hoarders. I don't keep shiz I don't intend to use on my computer. When I watch a television series, I delete it after I'm done. If I need it again I'll reacquire it. I don't keep games I don't play on my computer.
When I buy a new desktop I'll probably get whatever the standard size HDD is at the time, probably around the 2+ TB range. I might loosen my belt a little then, but most people are just bad organizers and prioritizes.