Headstock design, from a buyers standpoint, does seem to revolve much more around an aesthetic than it does around functionality. But then how many of us are quick to cry foul about a bass that will take a neck dive? That's something that can be very much attributable to headstock design and directly impacts how a bass will balance when have it strapped on.
When you look at the design of Fender basses from the 1950's and 1960's you'll find some interesting things. Notably, there are similarities in design between Fender's offerings and automobile designs. It would start with flowing lines that were reminiscent of sports cars, to chrome hardware and even the colors of bodies and headstocks. Some Fender colors came straight from GM's and Ford's color charts.
From a functionality standpoint, the Fender headstock works. You've got easy access to the tuners and it balances well. Plus the lines flow well. And like some of the other posters have mentioned that headstock is like a trademark for Fender. Granted, they were not able to trademark it in a court of law. But there is a definite association of that design with Fender. And that headstock design has been featured on almost all of Fender's most popular models at one time or another: P-Bass, J-Bass, Strat, Jaguar, Jazz Master, and even some Telecasters. Fender's history as a brand means a lot to a good number of people.
Ultimately, some of it does come down to personal tastes. Look at the aforementioned cars: some people are more influenced to buy a car for it's performance or functionality, and some people will seek out another car and base their decision primarily on aesthetics. There is a market for both. I think the most successful businesses will offer something that has a great blend of both: functionality plus a pleasing aesthetic.