Apple didn't release the Mac Pro (Early 2008) on New Years Day that year. It is possible that the poster could have bought the 8-core predecessor model before that Mac Pro was released while still buying it within the 2008 calendar year. Given that the Early 2008 model is just above the cutoff for Mountain Lion whereas the original 8-core is just below it, it is possible that the poster is using a Mac that isn't supported by Mountain Lion.