Racer Ex 

Seated you're not going to see much difference between cleats and not, because of the plane where you leverage power into the stroke. Any upstroke is barely supported. Pull up and there's not much holding you down.

Where you see a difference is out of the saddle where you change the leverage points and plane and gain a lot more support. This was pretty evident in my infamous loafer race where I was pretty much "there" until the sprint and on the OOS climbs.

Aside from OOS the biggest thing with cleats is that it allows (if you have float), a more natural foot/knee/leg alignment as you move through the stroke. Go out and run and you'll notice some slip in your foot against the surface you're running on.

As far as anything Rivendell wrote, they don't have a clue about bio mechanics and are just spewing dogma to sell product. Look at their old catalogs and when they had a big stock of non-Japanese made parts they bad mouthed Japanese stuff. When they ran out they started selling NOS Japanese parts as the greatest thing since sex. They'll gladly sell you a $9.99 Walmart button down for $34.99 as the "perfect" cycling shirt. They're all schtick and crap.