Hmm, I wonder...

A tube makes the effective width of the tire thicker--as in, if you were to take a knife and cut into the side of the tire, you'd have a millimeter or two for the tire, then another for the tube, before you cut through both. There may not be friction between the tube and the tire, but as the tire rolls, the weight of the bike+rider does cause the sidewall to distort at the contact patch (where the rubber meets the road). Higher tire pressure and thicker sidewalls should be less deflection for a given weight. Less deflection should be less frictional loss in the wheel.

So, I guess I could buy that a tubeless tire could be less friction. I have not looked at such creatures though, and I wouldn't be surprised if the sidewall was thicker. I also doubt that the effect is that noticable. If it were me, I'm guessing that $2600 would be better spent by spending only $1k on a bike and the rest on a personal trainer and on weight loss, rather than a faster bike.