Throughout the 1980s and 1990s, personal computing hardware continuously lept while software lagged behind. Applications grew to fill the space available because it was easier, faster, and more cost-effective to focus on adding features and not optimizing code. (I remember older programmers shaking their heads at the profligate use of RAM.)
Now applications take up hundreds of megabytes of space or more and require multi-gigahertz machines with a half a gig of RAM. But hardware configurations will be taking a u-turn. A cheap machine must skimp on CPU speed, RAM, and hard drive size to be economically viable. Engineers will design machines to run a browser and email software and eliminate the costlier configurations that have become necessary for long-bloated traditional apps.
The prices of these new machines will be tempting and greater numbers will migrate to them, especially as the economy continues to feel pressure. Need and machine configuration will combine, as always, to direct software usage. Users will have to increasingly look for applications on the web, because that will be the only practical way to run them. So even if cloud computing didn't exist, consumer pocketbooks would force its invention.
Cloud gate image via Flickr user RcktManIL, CC 2.0.