The difference is is that PS users and XBOX users paid the same amount for unequal product.
It isn't like you paid for your Skyrim content and THEN had to wait a year for it. As it has been said before, console exclusive titles =\= exclusive content for paid DLC. If they charged XBOX users less for the reduced content, that would still suck but would be more fair.
As an aside, you would think that the disappointing size of the game would encourage Bungie to hustle out more content to keep its player base up until the first DLC, and perhaps speed up release of exclusive content to the other platform.