There are several aspects. I knew that federal highway funds are grants for the purpose of making highways to the interstate standards (eg, landing strips), but also conditional on various things, most famously the 55 speed limit. I thought federal school funding was like that. I am fairly surprised to learn that RTTT was zero-sum, but since it was part of the stimulus, I'm not sure that's very informative. I am still unclear on whether the states proposed things to spend the money on, or whether it was an unrestricted prize for winning the contest.