Growth isnt everything, especially with antitrust people waiting to pounce
I guess if a companies only goal was growth or market share this would be valid. But in the case of Microsoft, growth like Apple has would be beaten down by antitrust lawyers in the US and in the EU, and massive growth of market share is not something they really need. Its more important to perfect the product and give "ease of use" and NUI to the users, than grow the company.
Heck, they might even try to split the company in pieces, god forbid!
Being #3 in smartphones, and #2 in tablets is not such a bad thing, it makes MS designers work harder, and competition is healthy!