This one is actually interesting.

They put water (1.8 L = 1.8 kg = 4 lbs) in the tires or on the bike (or no where) and climbed Alpe D'Huez.

You see a 1.3% difference between having the water in the wheels than just on the bike. If you take the different power for the run into account, the difference drops to 0.6% (or so).

This is similar to what I suggested by putting weight on the spokes, except that

(1) I wonder how much the water affects rolling resistance (I'm assuming the pumped the tires up to the same pressure) and

(2) since there is air in the tire as well, then the water is sloshing to some degree. I wonder what affect that had.

They didn't state how much the rider and the bike weighed. But given that they added 4 lbs and saw such a minimal difference (call it 1.3% if you don't like the 0.6%), this anecdotal evidence, I think this shows the magnitude of the problem of "heavy tires" (and I'm willing to bet that the combination of this rider and his bike are lighter than probably any of us having this discussion).

This one, not so much. They didn't make sure they had the same tires on both bikes (we know rolling resistance makes a big difference), nor make sure they had the same aerodynamic profile (depending on rider speed, this could be pretty much the biggest difference we're going to see).