-- Are "spot colors" the thing to use to get a grip on these matters?
No, because spot colors are used to extend the printable range by colors not available in cmyk. You might be able to show such a color on your monitor, but not print it.
-- Is this generally only a matter of "color spaces" and transformations between them?
Yes, because your monitor uses RGB and your printer uses CMYK. The conversion between thetwo is not too complicated, but actually getting the same output from the two is hard. RGB is an additive model, CMYK is subtractive (read about the different models, wikipedia will do). The color impression you get by looking at the output is generated in completely different ways. or ...
-- Is this also dependent on specific printer models (eg. different office laser printers)? -- If yes, is there any source on information on the pecularities of these printers?
Each printer will print slightly different, that's the nature of things. Your best bet is to calibrate your monitor (also, search a bit on the web for ways to do this). Turn a few of your monitors knobs and see how the colors change - now imagine what variables come into play between your impression of the color shown by your monitor, the actual data, and the impression you get from your printer's output! You can also try specifying a color in CMYK and see if the output changes. Regards Christoph