Earlier quoted context omitted.
Most OS have the possibility to adjust screen dot pitch (ppi, pixels per inch). Using a "high resolution" display (like my 23"@2048x1152, or an Apple "retina" display). Technically, setting your font to be eg 14 points, should be an absolute size - the same font should be the same dimensions (in mm/inches) on all displays. Now, you probably hold your smartphone closer to your face than you sit to your 30" LCD screen…
On Windows, devs rarely care about DPI issues, largely because they either never heard about the problems, thought "oh my GUI abstraction will take care of it" or think that the market share of non-standard DPI settings is too low.
Android does not have this problem since devs always use dp (density independent pixel) as units of measurement and OEMs choose good DPI values when they are releasing devices.
Although less gracefully, iOS solves this problem too (by doubling the resolution and scaling everything by two).