It doesn't seem like it would be that hard to add a time on page metric before counting pages, especially when you own the hardware. I am honestly quite surprised this was missed.
Even easier (or as a first step), Amazon could count the pages that were actually displayed, not the ones that were skipped past. I'm pretty surprised they're not doing that already since it would be a good way to account for books of short stories where a reader might skip over some stories naturally.