Exactly! And with five custom settings, you'ed pretty much be set for...anything.
I guess I've never used the custom settings so I don't know what they can do. Not having them on my cameras could be the root cause.
They let you choose...pretty much any setting, such as AF settings, metering settings, etc. including mode (Av, Tv, M, B), save it to a custom user mode profile. You can then switch to that profile simply by moving the mode dial to C1-N (some cameras only have C1, some have C1-3). I guess technically speaking, you would still need some way of choosing Av, Tv, M or B so you could save it when saving a custom user mode...that could be on the mode dial.
If you had a bunch of custom modes, though, you could then set up several Av modes with different AF settings...one for slower moving subjects, one for fast moving subjects, one for erratically moving subjects, one for still landscapes, and one other for say portraiture. Then it would be a simple matter of switching to the right custom mode to instantly change all the camera settings for whatever it is your shooting. The 7D, 5D III, and 1D X all have C1-3. I believe the 6D only has one custom mode.