Regarding Hulu/Netflix, Microsoft would certainly have its work cut out to keep contracts and gain new ones. But they have the money to, and it's going to be a loss leader to get people to buy other things, like Xbox or in the future their cell phones. Microsoft already co-owns a network with NBC (MSNBC) so maybe they have enough connections to make TV contracts.
Pandora/Spotify are bleeding money because of the royalty structure. It's maybe a coin toss if the rates will change. A matter the congress can decide. I think it's worth the gamble. Plus they could leverage this on Xbox too as well as phones.
These businesses aren't that profitable which is why I think it makes sense to buy them. Microsoft if they bought all these companies (and if the SEC would allow) would greatly expand their ad network and open up possibilities for new integrations and businesses. Every other major tech company (Google, Amazon, Apple) has audio/video. Microsoft should want to compete too. I don't see MS Word and being able to run EXEs as enough reason to go Microsoft. I'm imagining them unlocking a wholly integrated entertainment setup.
Also, I see MySpace being what it once was. A place to friend all the weird and interesting strangers and follow new bands. It was great for that and a lot of fun. Social networks weren't all serious like they were before Facebook and LinkedIn.