No, you do not. The difference here is that skills like florentine and style master don't continue to ramp up. You purchase them once and that's it. With Crit attack and Weapon prof (and back attack and backstab), you must first purchase 4 of the lesser skill in order to purchase one of the greater skill.
When you do, it converts the 4 times per day of +1 damage into a permanent +1 damage.
At this point, your character card will say crit attack X 0 and weapon proficiency X 1. You can then purchase crit attacks again to ramp up to another weapon proficiency.
You see, underneath all that, you never lose the skill Crit Attack. It's always on your card. When you purchase Style master, Florentine is removed from your card. You don't need it to be there so it serves no purpose, whereas the ramp skills always have a purpose, whether you ever decide to buy more profs or not.