In practice, many cyclists have observed that their speeds are slower with poorer rolling tires or poorer quality hubs and have decided to attribute it to weight.

The effect of the weight is both very easily quantifiable and accurate.

You can notice a huge effect between a good and bad rolling tire. The average rider here would not notice such an effect for different weights.

Seriously, why not just start saying that your tires with white reflective letters on the side are faster than those without (probably true, one average since higher end tires are more likely to have it)?