You are so right.
Pretend I am your GM, and I emailed you the following memorandum: " So, yeah, you guys are taking too much of my time rolling all those d20 to-hit/damage checks, so I have decided that from now on, everyone except tempest rangers shall only hit on a 4+ (d20), and said rangers (the worsts offenders) shall only hit on a 5+ (d20)...and oh yes, I will still roll for monsters d20 to-hit checks at the usual 2-20...but this is going to be really cool, because it will improve Game Balance, and make the game more FUN! "
Would anyone here be cool with that nugget of Fun-by-Tyranny? because that is exactly what a 10% reduction in DPS means.
But then again, the above translation is not quite right either, because even on a "4 up" (or "5 up" in the case of tempest) hit check, you still had a CHANCE to roll a natural 20 for critical hit on 1, 2, or 3, (and 4 for tempest) where as eliminating the dice rolls altogether (a la nerfdate 5) eliminates 2 or 3 dice rolls altogether, so you loose even the CHANCE to roll a natural 20..and that does not even look at the elimination of Attack Speed Boosts and the extra dice rolls they are supposed to generate.
How is this acceptable to any player?
That fundamental chance to roll a 20 is vital: it represents the wildcard "Joker"--that remote but ever present random chance of good fortune that ones' actions can prevail in the worst circumstances in spite of all odds.
Call it "mystical cleverness bereft of reason", or "favor of the gods", or just call it "necessary exception that proves the rule", whatever you call it, that dice roll (i.e. the small chance to jackpot) is our direct interface to "heroic" in DnD.
When you eliminate that, you eliminate the whole point of heroic fantasy.
Clearly that principle is no longer a relevant consideration in DDO.