You make a interesting observation. I think the reason it seems so popular right now is because every web app created these days caters to creatives/freelancers/webmasters. So they circulate in this area a lot. I mean I can name 20 different time tracking, invoicing, and project collaboration apps.

I see less "web apps" and more "consumer applications" in the next few years. Online software that is set out to meet a certain need in our lives.