That's a no display HP tower compared to a full system on the iMac. Maybe this cute little thing is more a direct comparison? http://www.apple.com/mac-mini/
the $799 one is quad core Intel.
So we're looking at more like a $200 difference, not a $700 one. Not to mention, with wi-fi, USB3, HDMI and Thunderbolt connectivity, you are good to go.