I wondered this once my self not too long ago. I searched and all I could find was lots of people repeating "the power company only charges for watts" like parrots with a traumatic brain injury and exactly zero people actually testing it.
Until now...
http://ecorenovator.org/forum/36999-post7.html
http://ecorenovator.org/forum/37998-post13.html
Sadly my simple tests are the most advanced residential meter testing to be found on the internet.
I have a very simple reproducible test showing that the power company's electromechanical power meter does read VoltAmps and I have first hand observations on digital meters showing multiple billing parameters that can only be a low power factor counter.
Now I have tested 70kw and smaller diesel generators on an advanced load bank that can test both KVA and KW. I know how reactive power really effects the load on the prime mover and believe the power company has every right to charge for VoltAmps, I think they would be stupid not to.
I would be flipping switches on the load bank with my left hand and had the Cummins engine analyzer showing real time engine load and fuel consumption in my other hand. It doesn't get any more clear than that.