With the exception of school books where the instructor needs to reference a specific page, page numbers in eBooks are unnecessary and confusing. It would be better for the reader software to calculate the approximate number of screens needed for the entire book then reference that as Screen x of y. As @Papi suggests, it could easily recalculate if you change the text size. That is how the decade old PDA reader software typically worked. With todays fast processors doing the calculation only takes moments and could be done in the background. Perhaps the optimum screenization system--a play on the word pagination--would be to display Screen x of y, zzz% read. That would give me at a glance all the information I need.

Making references in eBooks does not require an accurate page or screen number with the possible exception of classroom references. Most eBook readers have a search function that will find any reference someone gives you. Most eBook readers support Tables of Content that will at least get you in the ballpark, so to speak. And if a publisher is totally anal about letting you know what "printed version page number" you are on, let them hardcode it into the eBook.

And @doreenjoy is absolutely correct in that the Kindle system does little more than confuse people. It does at least give a percentage read number and status bar, so that helps.