@Kernal: Let me use your example:
Enemy (+5) attacks player (AC 19). Tie goes to the attacker (the roller), so the enemy would need a 14+, which is a 35/65 hit/miss ratio.
Players Roll Defense Check
Player defends (AC 19 or +9) an enemy's attack (+5 or DC 17). Tie goes to the defender (the roller), so the player would need a 8+, which is a 65/35 success/failure ratio (or miss/hit ratio).
By just using the defense bonus (+9) instead of the actual defense (AC 19), you can reduce the defense check by 10 from +22 to +12 (not +21 or +11).
For the record, the players rolling defense check was not an idea I had that was supposed to speed up combat.
You bring up an interesting point about Damage Reduction (or Resist in 4E). However, can you provide some real examples of enemies that have Resist so we can compare the Resist value with the static damage for a character of an appropriate level.