Horoku, that effect still exists. That wererat would have DR10/silver or DR 15/silver - so unless the fighter was wieldign a SILVER mace ... the description would hold just fine!
Let's say the fighter has a normal mace, rolls average damage, and is NOT a max-strength, raging barbarian and/or halforc. He'd do, say, 1d8+3 damage (1d8+5 if he's specialised). That means 7-8 average damage (9-10 if specialised), which bounces off the DR 10/silver of an afflicted lycanthrope.
The trick is, in 2E days - it didn't matter WHAT you did, nor HOW well you rolled, if you didn't have the right weapon, you coudl NEVER do even a SINGLE hitpoint of damage in combat with that were-rat.
Now, the fighter can hope for maximum damage (11hp, or 13 if specialised - gettign 1hp or 3hp through each time he does that) and a LOT of luck in NOT being hit, and he can pray for a critical hit, so that he rolls 2d8+6 or 2d8+10, averaging 15 or 19 damage, and getting a moderate amount "through" the DR.
The odds are, if the were-rat is a tough one, the Fighter will need HELP, in order to survive. But at least a single wererat can't kill an UNLIMITED number of first-to-fourth level characters.
Think about it: in the absence of magic weapons, silvered weapons, and spellcasters ... ONE werewolf could destroy an army of TEN THOUSAND warriors - assuming they didn't all just up and RUN, of course. Just one werewolf!
Now, at least, with good and well-trained warriors, equipped with good, high-damage (but still neither magical nor silvered) weapons ... there's a very high chance that, though losses might be very high, that army of non-enhanced, un-spellcaster-supported "normals" will take the werewolf down.
I prefer "it's going to be insanely hard to hurt this guy, 'cause your weapons don't seem to be very effective right now" to "you must be THIS HIGH to enter" nonsense.