But comparing it to desktop apps, mobile apps or console games, I would still say that web development has made it easier to do cross-platform development.

Sure you've got to support IE6 (mainly if you do enterprise stuff), but in desktop apps you have MacOS, Win7, WinXP, all Linux flavours. You can't make a cross-platform game (handheld or console). Mobile apps are divided in iOS, Android and probably WinMo7, webOS, RIM, ...