"So what does Microsoft want with Tremblay?"
Same as any other "distinguished engineer" or similar employed by Microsoft Research (eg Cutler of VMS and NT fame, Gordon Bell of PDP+VAX fame, C.A.R. Hoare of quicksort and CSP fame).
Bill wants to make sure these folk stay working inside/for the Wintel ecosystem rather than outside working (or speaking) against the Wintel folks.
It's a good return on investment for MS, to pay these good folks so much money that they couldn't really refuse it, even if it means they have to do nothing in particular except toe the Wintel party line while pursuing their own personal research interests.
Did it really need anything more explanation than that?