Why is the EM5 so much more popular than the GH3?

The GH3 is just an update to a previous model.  If the previous incarnations of this camera hasn't inspired people to join M4/3, the third version isn't going to raise any eyebrows either.

The E-M5 on the other hand is totally new, new body design, new IS, new sensor, and new bulb modes that have never existed before.

I had no intention of getting any M4/3 camera, the E-M5 changed that.  If the E-M5 hadn't come out, the GH3 wouldn't make me want to get an M4/3 camera, and I assume it's the same with all the Nikon and Canon owners who have jumped on the E-M5 bandwagon...I'd still be using my E-3 and E-330.