I think that the shortages are very real. Check the 360 Premium and Elite pages on BestBuy.com. Both say that store pick-up is unavailable, yet it IS available for the Arcade 360, and virtually every other item that Best Buy sells.
Take a look for yourselves:
Premium 360
Elite 360
Edit: As for the 10 closest GameStops in my area (ZIP Code 70001), 8 out of the 10 have Elites, but only 1 out of the 10 has Premiums.







