Doesn't using only 10+1/2 HD + SL result in weaker spell casters? It would seem to. For instance, with that equation, you would have to be 8th level to make a spell as hard to resist as someone with an 18 int (and few dedicated wizards still only have an 18 int by 8th level).
I was thinking the same thing (re: low-level casters). You could always alter the formula like so:
10+ SL + (1/2caster level OR Ability Mod, whichever is higher)
The ideal mathematical fixes to the published rules begin to make D&D into a Table Maze. I believe WOTC is trying to avoid turning the game into a series of endless table-lookups. These games die quickly because they emphasize precision over imagination.
No matter what happens to D&D's rules, its success will depend on its ability to foster the gamer's imagination. I think we'd all agree the goal is fine tuning the inevitable compromise, not producing ideal mathematical models for imaginary phenomena.
