FF titles where you purchased magic via Gil:
1/2/3/7/11

FF titles where you had to purchase them through something other than general experience gaining:
9/10/12/13

FF titles where you gained magic via exp:
4/5/6/8

(please correct me if I am wrong)

Either way, more often than not we have had to purchase our spells, i don't know where this idea of "we never had to buy them in any other FFs" is coming from. Maybe you've only played 1 Final Fantasy game besides this one? I don't know. But if my memory serves me correctly you will notice only 4 titles (and I was being generous by giving FF6 to the general exp, because its not really...but its ambiguous I believe) didn't have the purchasing of spells.

So that said, and since people are afraid they are not going to have enough money (I have no idea why anyone would think that with Leves giving insanely stupid amounts of gil vs their ease of access/completion) why not have ALL spells/abilities purchased via some points function? Ala, FFX/FFXII/FFXIII.