I had heard that porting everything would potentially lower the actual boost pressure you see, but not necessarily reduce power. The thought being that if you have a smooth setup you can flow better and therefore won't see the same sort of "backpressure" if you will, so the manifold pressure looks lower. However, since the pump is a pump (roots, turbo, centrifugal, etc.), if all the valves are closed, you'd see the same static pressure (whatever the pressurizing device is capable of). Dynamic pressure is a whole other animal and a little harder to get a feel for. There will be pumping losses associated with moving any fluid through any area. That would mean that you may potentially see a different pressure depending on where you put a gauge. Directly after the blower output may get you a marginally different pressure than right before the intake valve. However, boost numbers are so low and flow paths so short that I don't think you'd see much restriction. This is just stuff I remember from my engineering classes though, so I can't really say for sure how things actually work out in an engine.
Regardless, porting and such will always be of some benefit, regarless of induction type. In the case of a forced induction setup, you can potentially just use the advantage of a pressurized intake to overcome the inefficiency of the intake setup, but if you increase the efficiency of the flow, you won't have to work the blower as hard to begin with to move as much air. Changing a pulley or wastegate is likely way cheaper than porting your intake and head setup though, so it probably makes more sense to just put up with the flow losses of a less efficient intake runner.
To put it simply, you can blow X amount of air through a straw. If you have a bigger straw, you don't have to blow as hard to move the same amount of air. However, if you want to move more air and can't afford a bigger straw, you can just blow harder (within the limits of your lungs).
