Well, it's as the person I was replying to said: why buy a company that would work with you anyway. There is also the fact that Sony's talk of acquisitions started soon after E3 when Microsoft bought another company (after purchasing 5 others) and pledged to buy more. I'd think what you are saying would make more sense if this was a purchase that was unexpected, something that would expand their portfolio, but it's one they've worked a lot with and haven't other had a reason to purchase. It looks more like a defensive more than aggressively building their portfolio.
That said, I'm no expect on Sony's acquisitions so if you have more specific examples of what you are talking about then I'm open to hearing them.
Because it was expected, it is unlikely to be anything related to Microsoft, but it is pointless to debate because no one will ever know.
Well, if you look above we have at least Daniel Ahmad saying what I'm saying. That said, I fail to see how it being expected would mean it's not because of Microsoft. It was expected because Microsoft has been buying up studios and Sony has said soon after they will do the same. Again, if Sony was bolstering their portfolio then they wouldn't buy Insomniac because they work with Sony regardless. Thus, the only reason to spend the capital to buy them was to defend against someone else buying them.
And debating these things is kind of the fun of message board discussions.