The USP is the basis for all of the hammer fired pistols that followed it. What I mean is that they are all just modifications from it and are very similar in their form and function. As such, working on a P2000, P30 or HK45 is very familiar and easy if you have the basis down. Furthermore, all are rather robust in their construction.
The VP9/40 is still a robust pistol in complete form, but some of the internal components are a bit more fragile and it really was not designed to be repeatedly and easily disassembled and reassembled.