This preference could also depend on the font and what's rendering it; on my Thunderbolt Display, while "18pt" Consolas renders at less than 7 points wide using OS X defaults, Windows 8, using defaults for the same display, renders the same font at around 8.5 points wide by default, and Myriad Pro's "M" at nearly 13 points wide. Since 13/7 is approximately 18/10, your respective preferences may not be as different as you think.