I have a mod over at ubbdev which allows your user to adjust the font size on a per-page basis to what they feel is best, which would allow you to only have to maintain 1 copy of a style vs several for differant font-sizes.
Generally, only one copy of a style is created as they have to be updated and maintained; and when you get to users who create numerous styles, it can be quite a handful to make all of their styles (in my case, about 25 and growing) in several differant revisions.
You can also take and update the style yourself, it's fairly easy to do, just change the "font-size" element to whatever you feel comfortable with while editing the style through the style editor in the control panel.