At the core of EU "rules" is the prohibition on using market dominance to prevent other players in OTHER markets from doing their thing and competing there.
MSFT will have to first proof how they see the complaints as originating from abusing a dominance in the search market that Google has. The examples don't go there.
On the contrary: MSFT could easily be accused of abusing their dominance on the desktop OS to gain an unfair advantage in the search market by making bing the default search engine ...
I'd just love to see it snap back at MSFT. Their arrogant attitude luckily doesn't fly with the commission (the EU).