Well, the crucial adjustment is usually done during setup of the OS, when user is asked to adjust screen to his eyes. In doing so the OS will modify the ppi-setting, without mentioning it.
Later on user may wonder why things don't work as intended but won't connect the misbehaviour to the setup of OS. Instead will believe it's just a bug the software like excel comes with (though other software often doesn't like the modified ppi-setting as well). Therefore it's left like this, on top depending on the offset user maybe won't even regognize it. But in excel where the printarea only can be divided by entire cells, some millimeter can make a big difference. Therefore I guess most people don't know about and don't want to believe it if told so.

Anyway, concerning your new problem I must tell that I'm not an expert in doing printouts. So maybe others will share more advanced experience. For my part:
If you manually were setting pagebreaks and margins, I believe they should be shown on other computers the same way (maybe one printout is required to get excel to save the settings). In case you left the pagebreaks (and margins) to excel, there are a couple of other aspects to consider:
- Versions of excel (starting with version 2007 the compatibility of versions isn't anymore that granted as in former versions - though MS still tries to make people believe that)
- Printout and all related settings depend as well on the printer in use. Especially you must have a look at the settings about what kind of paper is choosen (e.g. Letter, A4, ... ).
- Have the computers installed the same OS? Especially if you mix Mac and Windows, they might not like each other (that's why Mac is using another ppi-setting by default - if I'm not mistaken)
- As ever, don't expect to much of excel when design is involved. If you adjusted printoutarea meticulously to the millimeter, I can imagine that on another computer the area easily can miss a column or row