By game play we mean in the broad sense. We do not alter the original arcade design or functionality with the sole exception of things mandated by licensing issues. The original Hangtime arcade ROM caps attribute points at 70 not 80. We even had our coder spend time reverse engineering to confirm this. To our knowledge there is only one version of the Hangtime arcade ROM, so if you saw differently you must've been playing a hack or a defective emulation.
From a design perspective we can only speculate what they were thinking, but this makes sense. If every sufficiently experienced player eventually arrived at the same all-maxed character it would homogenise the character customisation. By capping it short of 80 some subjectivity and individuality has to remain in all created characters.