Slot Array and Total Page Size
Where pages are used for internal purposes like sort runs, the maximum row size is 8094 bytes. For data pages, the maximum in-row size including internal row overhead is 8060 bytes.

Internal row overhead can expand significantly if certain engine features are in use.  For example, using sparse columns reduces the user-accessible data size to 8019 bytes.

The only example of external row overhead I know of up to SQL Server 2012 is the 14 bytes needed for versioned rows.  This external overhead brings the maximum space usage for a single row to 8074 bytes, plus 2 bytes for the single slot array entry, making 8076 bytes total. This is still 20 bytes short of the 8096 limit (8192 page size - 96 byte fixed header).

The most likely explanation is that the original 8060 byte limit left 34 bytes for future expansion, of which 14 were used for the row-versioning implementation.