I know that the temptation to "keep it simple" is there but, as someone who formerly had a 2-channel system and upgraded to a home theater receiver, I say keep an open mind. While people do report HDMI handshake problems, most of the time your devices (PS3, HTPC if you have one, whatever is next) will work just fine and you never have to change the input on your TV. Also in theory you can get better music sound quality if you connect your ipod digitally and let the receiver do the decoding.
Plus as others have pointed out, newer networked receivers have Pandora and Spotify built-in.
Finally as Arny K points out, 5.1s cost less than 2-channels these days (due to sales volume) so it's worth considering.
What price would you be paying for that Onkyo?