One thing I've noticed about the HL1 server roster is that a handful of servers use bots to fill in a user-defined amount of "empty slots." Valve some time ago added the feature on their server roster GUI to show whether a server has bots and I've noticed other game server tracking websites have added the option. I think this should be available on GameTracker. I get in some games there's no way to tell if they don't provide that information, but there are quite a few games that have a way to give server trackers that information.

But it does do that.

Go to a server page.
Below the Current Map image.
Based upon the last scan, there will be either two lines of information;

Current Players: 32 / 32
Average (past month): 27

Or if there are bots, then three lines of information;

Current Players: 2 / 20
Current Bots: 4
Average (past month): 4


Remember that the page information is only as good as the last evaluated server scan, and that may easily be a few minutes old.