While the $700M they just spent pales in comparison to the estimated $3-5 billion more they'd need to spend to actually build out a coast-to-coast wireless video network, it's hard to imagine why else Dish would have bid that much on the licenses. MocoNews has the lowdown on the story, including some speculation by the usual crop of analysts.
Personally, I'm not all that excited about mobile TV just yet. But I do like the idea of functionality - and price wars - that extend across all of the media I pay for monthly. Cell phone, TV, and Internet all for one reasonable rate? The ability to use my phone as a remote for my DVR and a laptop modem when I'm away from home? Sign me up.