There used to be a little spot underneath of the forums that would tell you who was active, who was a moderator, who was an administrator and how many people were on (surely some members remember that?). That was a nice feature but it got the boot a long time ago. I'm sure we'll have a feature like that in AG3 though.
I've answered this before, but a count of "active" users depends on a range of time (active today, this week, this month, etc). And generally, we don't publish those numbers.
Why wouldn't you publish those numbers? I wouldn't think it is to private and it would be a good addition for the site or even AG3.
That's their business. If you go into a store and ask how many customers they had today or how many products they have sold, chances are they wouldn't tell you.