Well, in the D20 DnD it basically goes:
Magic Thingy you can study for, like the bookworm type of mages. Study spells, learn new stuff thru reading and research and etc.
Magic thingy you got from some higher power. Do some rituals, rules of your own belief system etc... oh and they wear armor just as well as the average joe.
Magic thingy that comes naturally from your oen enlightenment and not studied for.
Well, since Int would not make sense when it comes to most force powers it would just be a choice of Wis or Cha. Personally I think Wis would be a reasonable choice as well, but I guess Cha is used cause it is much mroe balanced. Since Jedi already got the Wis to AC(defence) bonus from the Monks then linking force points to Wis would just result in massive Wis pumping. Now at least Cha would not be a dump stat.