As per the ePub 2.0 spec:

dtb:totalPageCount
Content: Non-negative integer indicating the number of pageTargets in the pageList. If there are no navigable pages, then dtb:totalPageCount must have a value of zero.
Occurrence: Required

dtb:maxPageNumber
Content: Non-negative integer indicating the largest value attribute on pageTarget in the pageList. If there are no navigable pages, then dtb:maxPageNumber must have a value of zero.
Occurrence: Required

As far as I know, dtb = digital talking book....so are these metadata values used strictly for accessibility reasons (audio books, etc?) Anyone have any insight on this one?

Yes, that is DTBook but there can be dtb pages in the TOC.NCX file. See NCX in the wiki