et's not forget that the "users online" is a 5 minute average synoptic of useage.
On PPRuNe it is actually 15 minutes.
How many requests are being processed at one time is also a function of the length of time it takes to process a request, which is why once things start getting bad on a web server they get really bad. That is why vBulletin (the software pprune uses) turns users away when the CPU load is above a certain figure.
An old Pentium system can indeed flood a T1 line, but not if it is doing tens of database queries to service each request.