AAAAARRRRRGGG!!! I've been noticing this highly useful feature not working and thinking there was a new bug. I would never have suspected anyone would have removed this on purpose - I use the membership list in groups all the time! I kind of depend on it.
Reading the other comments, it sounds like the thing that someone was trying to fix didn't really get fixed by sacrificing it anyway. But even if there was something gained, I don't get why you would have to go from one extreme - sending out update messages to everyone any time every other single member in the chat group logged in and out - to the other extreme - no update messages other than moderators ever at all. Couldn't a server somewhere collect a list of currently logged-in group members and periodically update everyone? The updates could be sent less often in the more extreme usage conditions. Our group chat membership lists wouldn't necessarily be accurate at any given time but at least we'd have _something_ that was hopefully when a few minutes or some time period of being accurate.