remember, the last few generations of old ladies have come from a time when that short, curled hairdo was fashionable - the weekly shampoo and set - the style is the same as in all those old photos from the 40s, 50s, 60s etc
same way most old men have short back and sides, as they did as a young man, so do old women keep the style they had most in their younger days
when this generation of people are old, their hair will probably be a lot more like they have it now.
same thing goes for clothes - the beige, the tan tights, the shirt and tie to do the gardening, the trilby, etc etc - all from their youth.
its not an old persons uniform, just that they have never adopted a new, more modern style
having said all that, it is also probably just easier to manage too.
I for one will never have short hair.