First off I want to start off by saying It wasn't fifty million bucks it was twenty five mill for three (Meaning seventy millon total)
Next, the contract was for 6 months, meaning that each of the DLCs that were "exclusive" won't be so in due time UNLESS MS does another deal with them and it is probably unlikely that any deal will be excepted given that they won't be making anymore money off them if they stay on the 360. They HAVE to branch out to get more money also, nothing is exclusive anymore when it comes to third party developers. For the longest time Metal Gear Solid Four has been touted as being for the PS3 only, the 360 version will have a version later this year. So, stop trusting the whole "it will only be on..." because in this time of age..the third party developers only say that because they are paid to, once the money train ends and they run out of cash from being exclusive, they branch out to get more.