Should there be more skill differentiation in terms of stats to focus on?

Right now pretty much every spell does flat damage and has a crit chance. Every melee attack is based off your weapon damage and has a crit chance.

There are of course a couple of exceptions. (incinerate... um... contagion...)

But why is this the case?

Why arnt there melee skills that do flat damage, or spells that scale from weapon damage?

Spells that dont crit?

Melee attacks that dont crit?

Skills that have a fixed attack speed AND dont crit?

Skills that use a hidden "shield damage" stat (like smite in diablo 2). etc?

Does anyone else feel like there should be more differentiation here than there is?

By adding these kinds of restrictions you allow the player to focus more on specific stats, which allows builds to do more interesting things.