Microsoft CEO Steve Ballmer used his keynote speech, during the open day of the company's Worldwide Partner Conference (WPC) in Washington, D.C., to insist that the rich client is here to stay.

A "rich client" isn't a deep-pocketed celebrity in desperate need of an expensive lawyer; it's a PC with a fatter processor and more robust functionality apart from a centralized server. A thin client, on the other hand, is a PC that needs the mother-like nurturing of a server (or another PC) in order to execute basic tasks.

"Many people, especially in corporate IT, they say we're only going to use thin clients," Ballmer told the audience at the Verizon Center, where Microsoft is hosting the WPC keynotes. "I don't believe that at all. I don't believe the cloud is a place where thin clients will take over. Again and again, we see the advantage of rich clients."

A rich-client device, Ballmer added, "can be higher performance; the rich device can do more on behalf of the user without network latency; the rich device saves bandwidth."

The thin client has been a continuous target for Ballmer. Way back in the summer of 2009, during Microsoft's annual Financial Analyst Meeting, he took aim at thin clients as a Trojan Horse for browser-based operating systems, specifically Google's Chrome OS.

"We have competitors who say they believe in thin clients," he told the assembled analysts. "What they are really saying is they believe in the browser operating system... But don't think there is some magic technology, [a] revolutionary thing that they believe in differently."

At the time, Ballmer also fired a shot at netbooks, insisting that customers wanted bigger screens. He suggested that a new line of ultrathin PCs would debut before 2010, providing lightweight computing at a presumably higher cost--and which would presumably run versions of Windows 7 that offered the company higher margins. "We want people to be able to get the advantages of lightweight performance and be able to spend more money with us," Ballmer told the analysts.

By running a higher-priced version of Windows 7, along with other software like Office 2010, rich clients offer Microsoft the chance to make more money. Despite Ballmer's insistence, however, I think thinner clients are here to stay: not only netbooks, which remain a staple of Microsoft's manufacturing partners' lineups, but also tablet PCs and more esoteric phone/tablet/PDAs like the Dell Streak.

Microsoft's already taken baby steps towards embracing the thin-client mentality--look at its Office Web Apps, which allow document viewing and (lightweight) editing via the browser. And its cloud initiatives are dominating this year's WPC.

But maintaining a market position in areas such as tablet PCs may demand a more radical step: stripping Windows 7 (and succeeding versions) into a lightweight, streamlined OS optimized for tablets and the like. If the recent Windows 8 rumors are true, they're already considering the idea; what's left is to take the step off the proverbial cliff. The alternative is to stay with the robust rich-client mentality, which may not jibe with an increasingly mobile future.