"Why is it that most people think road bikes are more efficient than mt. bikes? My personal vote is that they are not."

Because they are. You can rationalize your choices any way you want to, and come up with arguments that sound good, but very few people are winning road races on MTBs.

"Wouldn't the mtb deliver the power from the hub to the ground more efficiently than the road bike due to its shorter, and therefore stiffer (or more resistant to deflection, anyway), spokes?"

It doesn't matter, assuming, for the purposes of the argument, that there is any difference in spoke stiffness for that extra inch. The lighter weight of the road bike frame / components / rims / spokes / etc. allow the road bike to accelerate more quickly than the MTB, and the larger diameter wheels allow it to maintain that speed more easily. (You can find Brompton [EDIT: MOULTON] enthusiasts that will claim that their small-wheeled bikes are only kept from TDF victory by the UCI led conspiracy, but that's a whole other issue.)

"I've always been more comfortable on a mtb. Don't know if its the longer top tube, or the more upright seating position, or what it is, but there it is."

It's the upright seating position.

"I know seating and positioning are paramount to comfort and therefore efficiency, so this point probably is moot in my argument....."

No, seating and positioning are paramount to comfort OR efficiency. Very few of us would be comfortable for any length of time in the positions road racers maintain. This is why randonneurs and touring bikes are set up very differently from racing and track bikes.

"At any rate, the drivetrain can't possibly offer up much difference between road and mountain."

Yes, it most certainly can. At the basic level, most road bikes have higher gearing than most MTBs, which makes them faster on the flats and down hills. Then there's bottom bracket height, crank length, component weight, etc., etc., etc.

"The wheels maybe but the only real difference I see is the diameter. Seems to me that the smaller diameter wheel would be more efficient, but then I'm no rocket scientist engineer type."

No, there are additional differences between MTB and road bike wheels.

"The frame may account for some negligible difference as well, but, really, they're both about the same (at least when comparing apples to apples, i.e., steel to steel or carbon to carbon). Right?"

No. There's a reason MTBs and road bikes are built differently. The frames are built for fundamentally different purposes and are fundamentally, not negligibly, different.

If you're more comfortable on an upright MTB / townie style bike, awesome. So are many of us. But accept that it's a personal preference, and that these bikes, for road riding, are, generally speaking, in no way faster or more efficient than road bikes.