I might be wrong, but i don´t agree with you. When atc gives you a STAR, he´s not implying you´re cleared to descend at own discretion, i think you should maintain your level and wait until he cleares you, and if he takes too long, you can always report "ready for descent".
Bear in mind that atc will deliver the STAR as soon as you enter the FIR where the airport is located, which can happen many miles before you need to descend.