Linux rescued IBM, so it's a good move
You might want to read "Who says elephants can't dance" by Louis Gerstner (yes, that one). If it hadn't been for Linux and IBM's ability to virtualise, IBM would have died quite a while back.
It makes sense for IBM to re-acquire an Operating System - their OS/2 was not bad, but they got utterly shafted by Microsoft on it. Big Blue re-entering that market is going to make things a lot more interesting. It will also piss off Microsoft, which is always to be encouraged IMHO :)