The first two items have to do with auction revenue. Other than a few TV and radio licenses there just isn't that much spectrum to auction. The AWS-3 band is extremely unlikely to fetch this sort of money, unless they adopt the T-Mobile plan to combine the AWS-2 and AWS-3 in an asymetric auction. And there is no other available spectrum. It's like peak oil, but for spectrum.
And they include the same moronic "user fee" proposal that the Bush Administration included every year. This is like proposing several hundred million through "better enforcement" without explaining what you are going to do differently -- another common budget trick.
I may be wrong, but I would very much like to know what the basis of these budget projections are.
Budget here: http://www.whitehouse.gov/omb/assets/fy2010_new_era/A_New_Era_of_Responsibility2.pdf