The big difference: No scroll ball, different front buttons and HTC Sense, a custom Android user interface designed by HTC.
The Nexus One has been a flop from a sales perspective thus far, which hurts HTC more than it hurts Google.
Google has plenty of cash, and as far as Google is concerned, the Nexus One is about getting people to buy phones differently, not build a new business in the short term. It also provides a blueprint for other handset makers about what an Android phone can be.
HTC, on the other hand, doesn’t have the same lofty aspirations. It is a handset company. Building an excellent phone like the Nexus One, and not having it sell, is bad.
Unfortunately for HTC, it looks like the Desire will not be available in North America, according to Engadget. Maybe that was some sort of Google stipulation? Or maybe it’s just going to take another few months?