Indeed.  I was told that the decision was made based on testing and the tech outcomes with regard to performance v. cost.

The Pirelli tire had nearly identical characteristics as the Michelin they tested- yet Pirelli could supply them at a lower marginal cost.  Volvo feels that the new Pirelli is the best choice for an all weather tire for the particular characteristics that the cars are designed to handle.

I rare cases of supply shortage, Michelins' are used on the XC line.  Apparently there are early model 2003's with them that were produced during a Pirelli supply shortage.  

I have no idea what the difference in marginal cost really is... but needless to say- you get what they put on- no special requests.  Snow tires are a different story, but I believe that they are a dealer delivery item, not an FDC pickup option.

I didn't spend a great deal of time chatting about this- but I was curious because I have seen both the Conti's and the Michelin tires on Volvos here at our dealer....