The difference is MS wouldn't have to worry about another big publisher coming in, offering PG a huge contract to work on games for them instead. They're a proven studio, who consistently put out quality games. Even if you own the IP they've been working on, it's not that easy to just find a replacement for all those people working on it if they decide to take their business elsewhere.
I see your point however owning studios eat up the devisions budget and adds to the expenses. This means Playground will have to profit. MS have to now pay for all those enployees yearly. More studios doesnt always mean more money, it can lead to more games however if they dont make profit on there games they can go into the risk of closing or being sold out.
On the good side, they can be guaranteed exclusive games (which i dont care about exclusives) and MS can most likely fund more dollars directly to the studio to make bigger and better projects.
As it stands right now, Playground werent going anywhere and the freedom they have to make games is probably why there games are so good. I trust MS with there decision however to me, owning the IPs and hiring devs just seems more business smart if you view it from a buisness standpoint.
I do see Turn 10 and Playground Games partnership with each as one of the best duos in the industry. Maybe thats why this is comsidered by MS.
If true lets see how it pans out.