I'm pretty sure the characters all have different starting stats as well. Waaka would have high AGI, Auron STR, Yuna magic, and so on. Though 5 stat points here and there won't matter a ton, they are deffinately designed towards being different classes, but yeah they don't have to be fixed in the expert.
If you're curious, here are the two sphere grids.
Standard:
http://images.wikia.com/finalfantasy/images/9/94/Final_Fantasy_10_Sphere_Grid.svg
Expert:
http://i.imgur.com/UtyFI.jpg
http://i.imgur.com/ARlJM.gif
(Two pics of the expert one as neither of them are that clear)