Well, the fact that some people upgrade their fuel pumps/fuel systems when they go with NOS doesnt mean that NOS itself requires it.
Your fuel pump can only flow so much fuel, the stock fuel system/injectors, etc. can only deliver so much fuel. When you are maxing out fuel delivery because you are injecting so much air (ie, making alot of hp) then you will obviously need to upgrade the fuel system.
NOS might even be easier on the fuel system, as it doesnt require the pump to put out so much pressure, as raised boost. (ie, a fuel pump has to work hard to overcome 30+ PSI)
However, on a BPU++++ car that is already near maxing out the stock fuel, yes.. a fuel system is in order.
Now, if you ran the NOS fuel off a seperate fuel system of its own, then you can get by with running a good sized shot of NOS and not have to worry about fuel delivery.
There are many options. One option I'm currently looking at is NOS+Propane (both in gas form) for easy setup, and installation. Both are in the form of gas, plus upped octane of the propane make this a nice idea. Some viper guys run this, and I hear (not positive) that this setup is becoming known in the vette world as well. No need to worry about adding additional fuel capacity for the NOS+Propane, because its right there already.