Suits under the Sherman Antitrust Act have nothing to do with profit margins...only market share. While loosely defined in the Act, subsequent interpretations suggest that you need to have 2/3 of the market to be considered a monopoly. MS is a LONG way from having that. Indeed, I doubt they will ever have that kind of share in the tablet market.
That may or may not be true. I'm not a lawyer. But, when I used to work for Intel; Intel made processors and chipsets. Intel stated categorically that although they made motherboards and the processors that went with them, they had no interest at all in putting them together in a box and making a PC - due to anti-trust and anti-competitive allegatiosn that would surely follow. To this day, Intel makes chipsets and processors - yet will NEVER put them in a box and sell that box to the consumer.