Weird...it is very possible that I missed something ... but...
I think there are two types of Michelins:
Pilot Powers (street tire)
Power Races (Race tire (soft/med/hard compounds))
I've run both and I love them.
Difference is the compound and shaping of the tire.
The Power Races are more aggressive and turn in faster. Power races are also a race rubber compound, more prone to heat cycles, longer heating time, etc..
The pilot powers are a street tire, less prone to heat cycling, great in the rain, lots of tread, good mileage, and pretty sticky for a street tire.
Hope that helps.