It's been progressively updated (faster speeds, more reliable, more secure[1]) and in recent years, standardised (I think we're on the second version of the standard now) to enable interop/less interference between gear from different manufacturers.

[1] Yes, secure. Much like wifi, power lines do leave your house :), and despite claims to the contrary, the signal can be strong enough on the other side of circuit breakers/RCDs for it to be picked up by attackers (or neighbours). Hence encryption of the whole system.

Some forms of this are way older - X10 was developed in 1975!