I'm confused about the marketing on the new RPI 4. Here in the tech specs it says "Power over Ethernet (PoE) enabled (requires separate PoE HAT)". What does it mean it's enabled, but it needs a separate hat. The RPI 3 could be powered with POE using a hat, what makes this any different?
It means the hardware with a POE HAT will work without any special software changes needed. That means the support is built-in to Raspbian Buster (which was launched today with the RPi4).