The P182 has much better cable management options than the original P180. Basically, on the P182, you have a lot of space behind the motherboard tray to route all your cables enabling neat internals.
The P182 also has pre-drilled holes on the rear panel for watercooling hoses, and also has the built in fan controller switches on the rear, lower compartment and roof fans.
That's about it really.
Having said all that, the very latest P180's seem to be coming with exactly the same features as the P182, so they must have updated it.
If you definately want all the enhancements though, safest to order the P182.