Function. The strings should be as little angular at the 'nut' as possible... ie, the string friction needs to attain a certian level in order to vibrate properly,... but the angle behind/above the nut, if kept straight, minimises tuning difficulties, by derceasing bind. the tapered headstocks are an attempt to aesthetically do this... if you imagie a "v" pattern of tuners on a rectangle headstock... no go... But yeah... there is a definate size pref... I often dream of changing the headstock design to fit My aesthetic needs... really, it is an easy part of the guitar to change... Chop chop, and glue and peg on a new one!