For wiring, yes, you have to get under any layout for it to be done. To make things a little easier, Tim advises that once the bench work is built and before you put on the table top, pull all you main buss wiring around the benchwork. That can be done standing up while it is still fully accessible. That then pretty much leaves the hooking up of you track and accessories power feeds to the proper buss wires already installed.
Also, if you notice on Melgar's bench work, He installed casters so that the entire table was moveable. To make that size table move as one without flexing, addition supports to tie the legs together were added. On a fixed layout, there would not be that many lower supports so access would be easier.
