This is called going standby on an earlier flight in the US. While European airlines seem to frown on the practice, it's standard practice at most of the big airlines States-side.

The philosophy in Europe seems to be that if they allow it, nobody will ever buy refundable/changeable tickets. The philosophy in the US is that they'd rather get you to your destination sooner rather than later, because (1) it makes pax happy, and (2) it means there is one less passenger to worry about on the later flight if something goes wrong (delays, overbooking, etc.).

Glad to hear Easyjet is taking the passenger-friendly philosophy.