Back when you could change the font, what happened when the character widths were too divergent from the default font?
My understanding is that Apple failed to provide a dynamic layout engine for Mac OS X, meaning that every localisation needs a custom layout to deal with different word and sentence lengths. Whether this is still true, or was ever true, I have no idea, but I've never seen any indication of (Mac) OS X being able to lay out a window dynamically.
Changing the DPI in Windows still breaks a huge amount of programs (in the latest Skype installer for example, the "please do install crap on my PC" checkboxes can only be accessed by shift-tabbing into invisible controls that are lost due to static layout problems) while typical X11 desktops (GTK+ for example) have been dynamic layout for very long time. Even Psion EPOC32 palmtops had dynamically laid-out dialogs — you only have to state the controls you need, and the window is built for you. (EIKON dialogs were single-column, but OPL32 didn't have the means to add tabs to the window to get more controls in than would fit on the screen; it would have been as easy as dTab "New tab name".)
Example:
PROC confirm%:(pTitle$, pPrompt$) dInit pTitle$ dText "", pPrompt$, 0 dButtons "No", -(%n or $100 or $200), "Yes", (%y or $100 or $200) return (dialog = %y) ENDPNo need to create a window handle, window, lay out any controls, or anything. dInit begins a dialog box, and dialog executes it.