That's assuming they're intended to be roughly equivalent. I don't know if that's a reliable assumption. The most basic behavior (such as whether a PDF downloads, opens in a new window, or opens in the same window) can vary, so I don't think page numbers would be reliable, no. If they do offer that option, then they probably do use the same format, but I wouldn't be surprised at all if they don't.
I think most third party readers will try to emulate such a simple convention as page numbers.