Indeed. It's the same as their chrome gambit. Releasing chrome kicked the IE development team into gear and lit a fire under firefox's ass. Today if I launch any of the 3 most popular browsers on this machine each of them will score 100/100 on the acid 3 test and render it smoothly and seamlessly. That certainly wasn't the case when chrome 1.0 was released a bit more than 3 years ago. Now the installed base of folks who have truly modern browsers is vastly higher and the sort of browser-side capabilities one can safely assume when they build web apps is very much expanded.