First of all the "response time" is only one metric, and it isn't measured in a standardized way. Basically, a manufacturer can claim any response time number they want, and there's no way of really knowing--except for independent review sites, like
TFTCentral.
Secondly, input lag matters far more than response time anyway--response time measure how much ghosting there will be, while input lag measures how long it takes for the monitor to show the new frame pushed by the graphics card. The ZR2740w has a far superior input lag time than the Asus monitor, while still offering very good response time, so good that it's difficult to tell between the Asus and the HP during a test.