One way to look at this is to take a look at the building. It is the responsiblity of the GC, although the EC is wiring it.
For manholes, I have seen it go both ways. Larger projects I have seen the EC purchase and set the boxes, while the GC does the digging and grading.
I am on a project where there are a lot of manholes going in, possible more that 100 of them. The EC is digging, setting and regrading all of them. He has purchased some nice equipment.
I know this does not help you, but it may just put in perspective that it can go either way, depending on the project.