here are two important points to take away. First, as Ive often said, intelligent use of browser-based technology can accomplish more than most people realize. You cant do everything not by a long shot but for many of the things that information workers routinely do, even ordinary Web UI is good enough. And now Gmail is proving that we dont have to settle for ordinary.
Second, Gmails architecture is not limited to Web UI. Because it is protocol-driven, developers can create new tools that speak to the DataPack format. Many have done so already. My favorite spam filter, SpamBayes, isnt yet implemented for Gmail, but if that happens, Ill be sorely tempted to switch to Gmail full time.
So is Gmail a rich Internet application? Sure. Although that label most often applies to Java, .Net, and Flash clients, Gmail shows that Web clients can join the club too. But crucially, Gmails architecture is open to other kinds of rich clients, too. It doesnt have to be a zero-sum game.