Receivers are designed to be final destinations for audio signals, not too many of them have the extra and, for most situations and people, unnecessary feature of passing audio out through the HDMI. This is probably more a deal of choosing which features are important to the masses, and this one probably fell by the wayside. Hope this helps.
Mike
PS a suggestion may be to hook up an optical audio cable directly to your tv from the PS3 and just change the audio settings in the menu every time you want to use the tv for audio, a little inconvenient, but should work fine.