MS coming out early and aggressively helped a lot. Being the first next-gen console means that they have a head start on everybody else. The next big thing was MS's emphasis on NA. They knew that they just won't win with the 2nd and 3rd world countries against the Wii, since that console is a lot cheaper so they (wisely) concentraded on NA b/c it would offer a better return for their investments. Third, MS's emphasis on the online experience has really done them well. The online gaming, w/ dlc and such has a MUCH better profit margin than shipped games, b/c they don't have to monkey around with the physical content, shipment, purchasing of discs, etc. So this means more money coming back to MS than would be if they just had a so-so effort with the online stuff.
MS has shown that even though they have made a lot of half-baked decisions with the faulty 360, and I would even say the whole HD download premise of its next console which is nothing really special or even really an improvement as its current console has downloads, that they can act aggressively and really shake things up. Their inclusion of ANOTHER console in a year or two is going to shake things up whether sony wants to beleive it or not. Since this 720 thing will be coming out 3 years later than the 360, it is going to have the best hardware in terms of performance. So even though I don't really think that MS is going to make the best choices as far as its next console, you cannot say that the 720 won't be a big factor just as any other console at the least.