Yes, it leaves room for interpretation. I have always used the examples (which multiply strength bonuses on crits) to mean that any plusses to base damage count for crits. It is very specifically specified, everywhere extra dice appear, that extra dice are not multiplied. This seems to infer that only extra dice are not multiplied in crits, but other bonuses are.
Also, page 221 of the DMG 3.5E, under WEAPONS - Additional Damage Dice states: "Some magic weapons deal additional dice of damage. Unlike other modifiers to damage, additional dice of damage are not multiplied when the attacker scores a critical hit." It could be argued that by 'other modifiers to damage' they mean the inherent pluses of magic weapons (since a magic item has to be at least +1 to include other special eatures), but I believe due to wording everywhere that this is the general rule: extra dice are not multiplied for crits, but other modifiers to damage are.
My .02.
Aaron