Not a straw man - on a laptop away from readily available external monitors, it's quite common to want to see two things at once while doing work. We're discussing the line length policy for a single line of source code in a single file, not the number of characters that can visibly fit side by side on a screen.
There's definitely a bit more flexibility - not infinite - when you only consider the full-scale case. But one is often less productive with that as the only viable option, or else one has external monitors in which case in that usage pattern the laptop is effectively a desktop.