Why would the Air force need a "space truck" and not NASA?
Its easy to point the conspiracy theory finger when the military is involved. Especially when they are staying silent about what the plane's purpose is.
I haven't time at the moment to check, but I'd assume GPS and GLONASS birds are in geostationary orbit (or whatever they call that now), which would complicate matters significantly. I imagine the Air Force probably has some sort of weapon in mind for such cases, but I wouldn't begin to know how to guess what that is, except presumably a big rocket, whose payload is a small rocket, whose payload in turn is a tiny warhead with some very precise attitude jets.
NASA never wanted a "space truck". Ever see 2001: A Space Odyssey? NASA wanted something along the lines of the spaceplane/station/moonbase system depicted in the first act; the Space Shuttle program was all they could sell to Congress, largely thanks to the efforts of now-deceased then-Senator William Proxmire. (If you've ever heard a science-fiction fan curse that name and wondered why, now you know; if you want the full story, read the book whose URL I just edited into my prior comment.)
And, yes, "its [sic] easy to point the conspiracy theory finger when the military is involved." It's easy to do a lot of things, which is not the same as saying those things are sensible or worth doing; ignorance, especially of the trivially addressable sort, is no excuse for foolishness.
The Space Shuttle was designed to do several things that had nothing to do with NASA's purview: To launch anti-USSR spy satellites into polar orbit from Vandenberg, to reboost and repair those satellites, and to steal/recover USSR-owned spy satellites, taking them into the cargo bay and landing at a US runway in order to recover their technology in the event that the USSR got ahead of us again. This also applies to US-owned satellites at risk of reentering over the USSR to prevent their tech from catching up.
In order to do this, they made the whole thing incredibly expensive, and sacrificed a lot of capabilities NASA would have rather had.
That's what this is for. It serves as a functional military Shuttle analog against small payloads, and as a beta for a manned X-37C or X-37D against larger payloads.
To understand the X-37, you need a reasonable knowledge of the origins of the Space Shuttle program. The only reason that program came to even the bastardized fruition it did was because the Air Force signed on, and they did so only because they needed a means of servicing and maintaining their orbital equipment. In theory, and occasionally in practice, this means involved actual human astronauts going up and doing spanner work on satellites in orbit, but this was expensive and fraught with undue difficulty; cheaper and easier was simply to stuff the whole satellite into the Shuttle's payload bay and haul it back down the gravity well for repair, refit, and relaunch, and indeed many Space Shuttle missions involved precisely this evolution. (It's probable, if uncertain due to the Air Force's bent for secrecy with regard to their payloads, that the Shuttle was used to return some or most of these satellites to orbit; on the other hand, a Titan-IV's probably cheaper, and the Air Force has used plenty of those, too. I don't know much about what goes into that sort of decision.)
The X-37, then, far from being some kind of conspiracy-theory FOBS, is just a Space-Shuttle-style "space truck". The major difference is that technology has now reached a point where it's possible for such a vehicle to satisfy the Air Force's mission parameters without having to involve all the complex, costly, and potentially disastrous encumbrances required to carry living humans into space.
Edit! I've finally just recalled the name of the book from which I gained my understanding of the politicking which took the Space Shuttle program from initial conception to final operational "Space Transportation System". That book is The Space Shuttle Decision, published by NASA as part of the NASA History Series, and you can read it online at http://www.nss.org/resources/library/shuttledecision/ and, oh, probably lots of other places as well. A bit dry, but marvelously detailed and surprisingly objective given its origins; I recommend it unreservedly to anyone with an interest in the history of its subject matter.