How exactly can a warrior cast a spell? From the beta document, I notice the following:
Spell checks by other classes: Foolish warriors have been known to read magical scrolls in dangerous attempts to wield magic. A warrior, thief, or other character untrained in magic may attempt to cast a spell from magical instructions he encounters. Characters of untrained classes roll 1d10 for their spell check instead of 1d20, and they do not add any modifier for an ability score or caster level.
But it takes a 12 or higher to cast a spell, and that's just for a first level spell. How exactly, do you roll a 12 on a D10? Don't get me wrong, I have a player who can do just that, but let's ignore him for the moment.
The only way I see is to burn luck. Maybe a warrior in a last ditch situation could do this, but he's most likely better off burning luck for some other action, an attack roll or something. If the goal is to keep warriors from attempting spells, why have this mechanic at all? I suppose you could burn all your luck to try and cast charm person on the barmaid, or attempt to teleport away from Asmodeus or something. Is the design goal for just these rare and last ditch situations? If so, that's cool, I'm just interested in the design goal.