Google uses (and hosts free for everyone) jQuery. You can even use their new compiler to get a smaller version of jQuery. The widget library has some overlap with jQuery, but does so much more and has been in progress since well before jQuery UI (Google bought Writely in March 2006 and jQuery UI didn't come out until September 2007).
MS uses and hosts free too. what is your point? i'm talking about progressing current successful open source projects. fyi, its library has overlap with jquery core too!