http://www.geocities.com/sixospades/bg/stats.htm
And yes, you did nail the problem. Intelligence only alters the MAXIMUM number of spells that can LEARNED per level (and in TRUE D&D also decides the highest level of spell that character can cast... not implemented in BG Series). Any intelligence of 19 or above will let you learn every single spell in the game.
The higher the intelligence, the better the chance of scribing the scroll.