they arent - read most tests and difference between MPSS, GY Eagle F1s, Conti Sport contact 5s and even Hankook Ventus S1 Evo2 is negligable.
While MPSSs often win the dry grip test, GY and Hankook frequently perform better in the wet. Personally i went for Hankooks, get excellent reviews but since they're not a 'premium' top 4 brand (Michelin, Bridgestone, Pirelli, Continental) they're a lot cheaper.
http://www.tyrereviews.co.uk/Tyre-Tests/#summer