Although operationally there's not much of a difference between a cycle-accurate FPGA implementation and a cycle-accurate software implementation (especially on a board that you can plug into a hardware CPU socket[1]) the FPGA implementation is interesting to me because it seems closer to the original gate-level implementation in hardware, and because it seems more tangible. Of course a custom silicon implementation (such as a recent HN comment about a tiny tapeout reimplementation of the PDP-8[1]) seems even more real and exciting, even if the cycle/signal timing is the same. Part of it may be that the custom silicon implementation is a self-contained reimplementation rather than an emulation based on pre-existing, complex components.