From Arreat Summit:

Critical Strike and Deadly Strike have the same mechanics and only one of them can trigger on any given attack (so a player can't get quadruple damage)

Any chance Diablo III makes these things independent?

Example:
Agility gives you 23% chance to crit for x2 damage.
Skill gives you 17% chance to crit for x2 damage.
Item gives you 5% chance to crit for x3 damage.
would translate to

30.571% chance to crit for x2 damage.
3.1955% chance to crit for x3 damage.
3.7145% chance to crit for x4 damage.
1.6090% chance to crit for x6 damage.
0.1955% chance to crit for x12 damage.

Total chance to crit: 39.6765%

Then there could be a shrine that could give you another 25% (x2)
And a potion that could give you another 20% (x2)
And another potion could give you 1% (x5)