While I am not sure we are technically reading words faster, my mom and I are reading through books much quicker.
As others said, we find the consistent font and font size are much less tiring on the eyes than p-books. So we don't find ourselves pausing as often. Plus you can read the Kindle without adjusting to the size of the book or whether you are reading on the left side vs right side.
Also, we are both speed readers versus word-for-word readers...and with the Kindle, its much easier to do this. Not to mention we can quickly scan paragraphs that don't interest us or really add to the plot.
...like the love scenes in some of those fluffy novels my mom likes to read
Of course the problem is that I can't buy Kindle books fast enough to keep up with her habit given she is retired