At least, any differences are not so significant that AGM's require different charging equipment than that used for flooded cell batteries. This is from the Optima literature. Maybe other AGMs do have different requirements, I don't know.
Gel cells are different, for sure.
You have to charge gel cells slower than wet cells. I agree with the part about ease of replacement in remote locations. I don't see much of a problem with having a bank of AGMs and a bank of wet cells. I guess the thing that PS is trying to avoid is having a bank with multiple batteries and having one of those batteries go bad and not being able to replace it in some remote location. This month's Practical Sailor had a brief piece on batteries.