Thanks for all the responses.
I agree that perspective needs to be considered, and with the limited tools we have (i.e. lenses that focus light) it might be the most powerful tool in making miniatures look life sized.
I think some are underestimating the DoF issue however. Since we've all been looking at pictures since the day we popped into this world, we have an ingrained knowledge of how lenses render images, whether we realize it or not. That is why the T/S stuff is so powerful. It gives the effect of shallow DoF which is usually completely absent from pictures taken at such a distance, thus it feels like the camera must be 3 feet above a model. Similarly, if you could take a picture of a miniature where everything was f/64 sharp, I think you'd never question that it's life-sized, assuming the miniature itself is realistic enough (herein lies the practical need for good perspective). Perspective will be accepted automatically if there are no other obvious cues.
Anyways, no sense in beating a dead horse.
P.S. There's some famous movie studio that did a lot of miniature work in the 50's era, and there's a website out there somewhere... but apparently there's a formula that relates the scale of the model to how "slow motioned" it needs to be to look realistic. So, whereas a matchstick falling to the ground looks like just that, if it's slowed down enough, it'll seem like a 2x4!