3.0 DR was probably designed around average. I guess that when you faces a creature with 50/+3, the party was assumed to be at a level where some (but not all) of the characters had +3 weapons. So if for example half of the party had +3 weapons, the average DR would result in 25, while a slightly higher level party could have 3 +3 weapons in 4 (fighting) characters, with average 12.5.
Now if 1 of four has the adamantine weapon (just supposing that the others have bought different materials so that the whole party covers more monsters), he alone beats DR, and party average for DR 15 is 11.75.
The problem as a party it's probably about the same. It's very different for the individuals instead.
I think most players would just hate to find themselves in a fight where they cannot just hurt the monster, and here's why the majority prefers a lower DR even if it more difficult to overcome.
The bright side of not being able to hurt a monster is however that the player is forced to come up with creative ideas during that fight, instead of just soaking damage to the opponent.
One mechanical difference remains anyway. With the old DR, there was a grey (i.e. interesting) area around a certain party level, because if NONE of you had strong enough weapons then you had almost no chances, while if ALL of you had +3 or better, then DR was irrelevant.
With the new DR it's probably about as interesting at every level, because different materials have relatively low costs (at least, after a certain minimum level) but you cannot stack them, so if ONE of you has an adamantine weapon at level 5, it's not true that ALL of you will ever have one.
My conclusion is that both DR system work quite fine. For sheer style I prefer the new one, just because it's more flavor to deal with different materials or holy/unholy weapons instead of just a number. (It does have anyway a small balance drawback, in that it downgrades the usefulness of enchantments larger than +1).
That's a great quote.
