I don't think anyone means to omit the crew but it happens. Perhaps, it's because of the conceit that if you wear black backstage, you won't be seen. Who knows?

But, after a long weekend of shows, I realized how much easier a show is when the crew is competent and pleasant--a key trait when we're doing 5 shows in a weekend. Crew members can become like an ersatz family especially after spending 70-80 hours with them during tech. We become each other's sounding boards and drinking buddies--a post show beer is a great way to let off steam.
They can also make my job much easier. I no longer have to worry about setting up backstage, I can just ask my ASM (Eric Snell in this case) if props are set and if he says, "yes," I know they are set. I can also call on them to go above and beyond. Larry Fowler is the sound board operator and I've worked with him on several shows. During The Seafarer, I had to rehearse an understudy so he jumped in and helped set up backstage so I could continue to rehearse.
Oh, and by the way, neither Eric nor Larry complain much about what they have to do. They are like walking Nike commercials; they just do it.
A previous Assistant Stage Manager of mine, Alec Farrell is now Stage Managing at the Arden. But he still jumps in and helps me out whenever I need it. An actor was late for the show one night and he took my car to try to find him. It's that spirit of "What can I do to help things run smoother," that makes a production so pleasant to work on.

Unfortunately, the crew is not often recognized as much as they should be. Although, Maureen Torsney-Weir, the only actress in The History Boys, made a point of complimenting the entire crew when we were in the green room. She said that all of us worked so well together and that we all made the backstage a nice place to be.
I was so excited that she mentioned all of crew when she did that. So I'm joining Ms. Torsney-Weir and raising my pint to the crew! Cheers guys!