Prince gets a good amount of play on the Sirius XM 80's and 90's station (and probably the retro R&B/funk station too but I don't listen to that too much), even before his death. Plus of course there's a lot of crossover with dance music, remixes and such or DJs sneaking his stuff into their sets. Controversy closing a nu disco set = 
I'll admit that aside from Hallelujah I didn't know anything about Leonard Cohen, but he's not normally the kind of music I listen to or would be exposed to.
George Michael, you couldn't have lived through the 80's or early 90's without seeing the Faith or Freedom music videos. Hell, even Kelly Kapowski wouldn't shut up about him.
I don't listen to 80's on 8 or 90's on 9 on Sirius anymore. I found out a long time ago that the 80's station for example only ever played a special brand of pop and didn't represent the full spectrum of 80's music. That said, I listened to the rnb/soul stations and Prince never really popped up on those stations. I'm trying to remember a time they played Prince on the rnb/soul/funk stations and I'm drawing a massive blank. I grew up on listening to two different rnb stations, and the classic one that plays old hits and stuff never played Prince beyond Little Corvette, 1999, Kiss, and the occasional Purple Rain. Meanwhile, everyone played Michael from almost every era.
I never heard a single Leonard Cohen song before his death. Just not the type of music I'd listen to but he certainly seemed talented.
George Michael, I'm quite familiar with Faith and Freedom. Never saw the music videos growing up, but it was impossible not hearing Faith or Freedom once. Seems I'm familiar with his famous songs, but for me he was one of those artists where I'd know their song but not who did it.