Adding to Marco's answer, the value is most definitely affected. The way problem reduction algorithms work is that we often exploit problem information as it's processed to tighten variable bounds in real time, which of course affects the relaxation.
This not only means that problem reduction will often change variable bounds, but the exact changes depend on the reduction algorithms used and on the order in which the calculations were performed.
W.r.t. your second question, this value generally varies wildly, even among different versions of the same solver, because it's affected by many many things, e.g., domain reduction algorithms, convexity/integer cuts, whether the solver defaults to a non-linear relaxation (for MINLPs) etc.