Well compared to my Audio Technica studio headphone they sound like *censored*..

but all in all they're not all that bad.
I tested them using a test signal (sine sweep from 20-20000Hz) to see how high they go and was pleasantly surprised. They can reproduce everything from some 30Hz to 18kHz, which is more than adequate for music listening.
Still.. Razer should correct the info on the website ASAP. If they know anything about sound, they should know 20-11000Hz frequency response is ridiculous for any sound system today.