The initial mandate used a very unusual choice of words, which leaves a lot of room for interpretation. This may well have been deliberate - as it gave the option of switching sides if it looked like Gadaffi was going to regain popularity and power, but makes for a lot of uncertainty in how far we could go to start with.
The US having now backed the rebels as the 'legitimate source of power' in Libya releases a lot of Libyan govt cash for their use, making it possible for them to buy the sort of armaments they are lacking - probably from the US. Vested interest? What does that mean? ...