it is most likely the laws. For example in Canada, many contests aren't open to quebec citizens due to some laws in effect in that province. however, they get their own - they only have to wait
This is correct. Specifically the gambling laws. In the US it is gambling if you pay money to enter a game of chance for a substantial prize. Companies get around this with the "no purchase neccesary" line. In other countries the definition is any game of chance in which a sizeable valued prize is awarded. This differs from US laws because it does not require payment by the gambler to be considered gambling.
I am no legal expert but this seems like the proper reason.
It is interesting that this is for the retail version, and not a Collector's Edition (if there's such a version that'd be available; not saying there'd be much difference between the two except for the possibility that something extra in the box or possible ingame item might be available).
I wonder if a person was to win the lifetime subscription would be able to buy the collector's edition for it would be able to apply the game code from the CE version to the retail version awarded through this sweepstakes?