I suspect the reason for the "No Standby's" on E-Saver fares is that the E-Savers are offered on inconvenient (empty) flights.

The purpose of the E-Saver is to generate additional revenue. However, what was happening was that people like me who were buying weekend trips anyhow (at much higher fare), were shifting to E-Savers, and then crowding the gate for a stand-by for a more convenient flight. You always used to know it was an E-Saver flight, when there would be a mob of standby's hovering near the gate, and a gate agents who looked like they could use a stiff drink.

So before the "no-standby" policy, USAir was losing money on me (actually, making less than the would have). I'm just glad I was able to exploit the E-Saver for as long as I did.