Power - If you build it right the PC will use around 100 watts under load, less than a light bulb under most usage conditions and a few watts when sleeping.
100W for htpc??? Netgear uses 15W on load - 1-2W on standby
Remote - There are remotes that power on the system (I have one built into my case). There are also a bunch of alternatives to this (using smartphones, wake-on-lan, boot on keyboard/mouse, etc).
like I said - hacks, including one build into case, which by the way makes htpc build more restrictive and expensive
Noise - It is incredibly easy to build a PC that is silent using large fans at low RPM
Large fans don't feet into small htpc case. Yes, it's possible to find a fully silent platform & case - its not "incredibly easy"
HD Audio - Natively supports any HD Audio you need via bit streaming over HDMI.
By HD audio - I meant native bitstreaming of HD codecs like DTS-HD, nvidia still doesn't do this to my knowledge, only new (since 5xxx) ATI gpus do this
Fully functional HDMI port - No idea what this means. My HDMI port is as functional as they come
I had htpc with Nvidia Ion platform - I spent day trying to passthru audio thru it with no success and secondly the rgb range didn't match my monitor, which wasn't a problem with vga out. (0-255 vs 16-255)
Boot Speed - Fast boot options exist. I can get into windows in about 5 seconds. If I turn my HTPC and TV on at the same time, I'm in Windows before the TV can turn on completely. If you need to go any faster than that, you might want to free up your schedule