Hard drives aren't loud either way. The optical disk drives and fans are much louder. Capacity seems like a very important thing if you're going to be storing hundreds of hours of HD video. A single 2.5" drive seems totally unsuited.
And there's another thing about the Mac Mini: yeah its a tiny little minimalist thing, but now start attaching an external hard drive, an external blu-ray drive, external video input for DVR... now you have a mess of pods and cables, not sure why this would be considered better aesthetics than a single brushed aluminum A/V styled PC enclosure which looks like any surround sound receiver.