Microsoft is very unhappy with the EU's persistence when it comes to the amount of money they're being asked to shell out, to the point where they claim the EU's actions could result in Vista being delayed. Not only does the EU deny this, they deny that they are singling out Microsoft or that they have any sort of vendetta against them. Rather, the EU says they are looking to create an innovation-friendly market, and that their pursuits were legit in this fashion. Recently, Microsoft commented that the EU was "playing games", but they vehemently deny this:

"Far from pursuing a vendetta against Microsoft, the Commission's actions are guided by the desire to create the most innovation-friendly business climate in Europe to the ultimate benefit of European consumers," the EU Commissioner wrote in a letter published by the Financial Times.
Microsoft owes the EU record amounts after the Commission came to their final conclusions, and there could be even more in the future. A delay in Vista would definitely irk many businesses, and this may be a ploy by Microsoft to force their hand.