I'm not sure if there have been an errata on this on the 2nd printing of the MM (or even if there was a 2nd printing out), but shouldn't the green dragon have a Damage Reduction of 20/+3 when they are wyrms? As it stands currently (in the 1st printing of MM and the SRD), green wyrms is at a serious disadvantage against other wyrms (or creatures that requires a +3 weapon enhancement to bypass their damage reduction)...while white or black wyrms (decidedly weaker breed of dragon to the green) do not have such issues. 
