"The fact that changing your printer driver alters the formatting of a document kind of boggles my mind."
It boggled mine too -- at the time. But I can confirm that. Quite a while ago, a friend of mine (to whom I played the role of "local friendly hacker") upgraded from a dot matrix printer (360 dpi, remember those?) to an inkjet (300 dpi).
His carefully written tables kind of exploded :-)
Turns out that the internal measuring unit of Word used to be "whatever The Printer is able to resolve", in a typically Microsoftish nonchalant way.
So tab stops could, with some luck be at such points that the different resolution pushed some material one tab stop further -- some not.