I don't consider this a big deal. Audio decoding in the player is IMHO the "right thing(tm)" to do, HTPC isn't different. Until recently, HD DVD wasn't different.
For anything remotely interactive (PIP) the player must do the decoding & mixing.
So, IMHO the perfect player can decode all and everything (TruHD, DTS-HD, DTS-HD MA) and outputs 7.1 LPCM. HTPC can't do this yet (only analog), as ATI implemented a cheap HDMI audio output (idiots). Where is Nvidia when you need them?
The PS3 comes close, and with its processing power it should be easy to add DTS-HD / DTS-HD MA decoding. I don't know, if Sony will do this (would Fox release all titles with DTS-HD if Sony told them, they don't?), but I must say, that the 1.5MBit/s DTS core audio isn't so bad at all...
A Receiver / Amp with HD audio decoding may be "nice to have", but isn't really necessary.