Hi @couplewavylines,
There’s some info on the reasons for the 128ppu here 
[SOLVED] Snapping to Grid Problem
Nutshell - in one of the lectures Ben mentions about aiming for an iPad Air, and mentions its screen resolution, followed up by the research into how many blocks the original Arkanoid type game had across the screen. The question does come up quite frequently, so you are not alone. If you search for “128” in the search you’ll probably get a few more results too
Hope this is of help.