Pete,
I agree with what you're saying, and had the same misgivings myself initially. However, the one thing you
might be overlooking is location, location, location.

I.e., IF they have managed to secure a facility for their receiving antenna farm that is in close proximity to the transmitters, then they don't need to worry much about resonance and tuned antennas. I think most of us are aware of how it's possible to pick up stations that are strong enough and close enough, with nothing more than a paperclip. I see this as taking that principle to its logical extreme.
The other thing they are doing that differentiates their approach is to dedicate a tuner to each antenna. That's never been done in any MATV system that I'm aware of. Lastly, your comment that 'the users are sharing the output' is incorrect. If I'm renting a dedicated antenna, dedicated tuner, and dedicated network interface, that data stream is available to no one but myself. Just the same as my dedicated 15' high antenna (volume ~2x3x1') located 50 miles from the towers feeds my dedicated HDHomerun tuner(s), and provides a networked datastream exclusively to me.
Personally I'm more uncertain of the financial aspects than the legal or technological ones. I don't even have a single 15 MBit/sec WAN stream coming into my home (though I could). But, I can easily stream and record 6 channels of 15 MBit/sec from my 3 dual-HDHR modules,
at a monthly cost of $0. I honestly can't see how renting even 2 feeds from Aereo could be cost-effective... much less more of them. And you do need a dedicated feed for every channel you want to watch or record at the same time. For most people, one will not suffice, and 2 (or 3) will be required.
As for Aereo's 'reticence' to explain their system, perhaps they have patents pending that they'd prefer to give some time. Or additional patents they're still preparing. Or maybe they simply felt there was no benefit to them in explaining it to you (or me).
- Tim