This is actually one of my biggest disappointments with the Hyperloop announcement. Musk said early on that it wasn't a vacuum tube. But in the end, we have a tube with vacuum pumps, and an air pressure much lower than that of Mars. In my book, that is close enough to a vacuum tube that it sounds like purposeful mis-direction on Musk's part. I.e., when he said (when he first mentioned the idea) that it isn't a vacuum tube, it would have been more honest to say that it isn't a complete hard vacuum tube. Would have cut out on some of the more wild speculations.
"Vacuum tube", aside from being a complete misnomer that's more usually applied to 'pneumatic tube', betrays the concept in one particular area:
It's a battery-powered hovercraft inside of a soft vacuum tube (soft vacuum being within reasonable reach of cheap pumps), with boost segments to get it up to speed.
Usually, vacuum concepts rely purely magnetic levitation & propulsion. The fact that it's an air cushion vehicle in a soft vacuum IS the novel concept here.
I think it would be misleading to call it a vacuum tube, since there are well known implementations of that where the capsule is moved by air pressure/vacuum. Meanwhile the hyperloop has electric propulsion. If he had said vacuum tube, no one would have guessed the propulsion mechanism. The air pressure being reduced in the tube is done more for efficiency than as the mechanism of movement.
While it might seem like a vacume the amount of air left in the tube makes it far cheaper to operate. It's one of those 1 +/- .001 foot rod is not that expencive but a 1 +/- .0001 foot rod is getting there and a 1 +/- .00001 foot rod even more so. Basicly vacume pumps cost more, use more energy, become more delicate, and move less air the closer you get to hard vacume.
However, there is still plenty of air in the tube to be an issue at the proposed speeds thus making Hyperloop cheaper and more complex than a traditional vacume transport.
But isn't the fact that it is not a vacuum an important aspect of the design? First, some air is used to elevate the train. Second, it's easier to maintain a near vacuum than a total vacuum.