It is not true for all HDMI receivers, but it is a common limitation of lower-cost receivers and has been a common issue with HDMI switching since the 990 was new on the scene (it's actually one reason that Outlaw chose the DVI connector for their DVI/HDMI switching - they didn't want people assuming it would do HDMI audio and getting pissed when it didn't). If you look at the fine print somewhere in the Denon manual, it will mention that the receiver (which may very well sport "HDMI v1.3" support) offers HDMI video switching and audio pass-through only, with no support for audio input via HDMI. More expensive models add support for audio via HDMI.

This is one reason that I've complained often in the past about HDMI's approach to licensing. I've long said that they needed to have a sub-set specifically for HDMI switching (even if was solely a matter of sticking a little "S" superscript or subscript into the HDMI logo on such products).