So 37% of current owners need to buy one of the DLC packs to make he 50 mil back.  When you put the 2.5 mil into a % of owners it seems quite high.  I'm sure that will fall over time and there will be plenty of people who buy the game for 360 when DLC is released.  As said by others it is also possible for the DLC to be boxed with the game if sales are low (would probably be done after both DLC packs are released).  So it does seem to be a high % of players but I certainly think it is within reach for MSFT to make that money back.  Was it a good move? Maybe, it certainly would help relations with Take 2 for MSFT's developers.  As for helping the game to sell over the PS3 version, that has yet to be seen.  The PS3 seems to have better adoption than the 360 version in WW sales. 

I can see that 2,500,000 x $20 = $50 mill but the MS points need to be purchased from a retailer and the retailer gets a percentage.  Also Gamestop is selling DLC coupons so once again the retailer will have to take a portion.