Philip said:
I don't think my reading of the rules is the right one, I only want to suggest that it is the most plausible one. Read p. 222 3.5 DMG again, second sentence: 'Each +1 of enhancement bonus ALSO adds 1 to the ....'
This 'also' clearly implies that both statements can and should be read separate from each other, and thus your reading that the (contradicting) hit points and hardness rule described there is an exception which is only used when resolving weapon vs. weapon damage is not likely.
Additionally, 3.0 and 3.5 tried to simplify and unify the rules, making it easier to apply it. Such an expection would make it harder, and thus contrary to the general philosophy.
Furthermore, it makes more sense to read it my way. Why should a Storm Giant with his +1 sword not be able to make a single scratch on that +2 quarterstaff? Why do older dragons even have Improved Sunder? It's not like they have to fear anything from normal weapons.
With its change in DR the 3.5 game also left the notion that a difference in plusses has any qualitative effect. Your interpretation also conflicts with that notion.
And lastly, it makes is easier in for me in my game, which is to me (and maybe to others) the best argument to consider the paragraph on p. 222 3.5 DMG an oversight and error contradicted by rules elsewhere.
Taking these one at a time...
1) I simply don't agree with the weight you attach to "also".
2) There may be magical forces that can destroy magic weapons (the disintigrate spell comes to mind) so that hardness and hitpoints have uses, even on my interpretation, aside from measuring how to determine how much damage a magic weapon can take from magic weapons of equal or greater plusses. Thus my interpretation does not require that hit points and hardness are of such limited use as you imply my interpretation requires.
3) I don't find my interpretation to be that complicated. From a bookkeeping point of view, it is easier, since you don't have to keep track of a weapon's hit points if your opponent has nothing that can sunder it.
4) A Storm Giant with a +1 sword can't scratch the +2 quarterstaff because the quarterstaff is made of mightier stuff. It's magic. If one wants to bring in "Realism" one might want to explain why the same Storm Giant does not collapse under his own weight, or at least break his ankles with his first two steps.
5) Why do dragons have improved sunder? Perhaps they like to break non-magical things. Perhaps they like to break wands, staffs, holy symbols, and other breakable goodies. But my interpretation does explain why they have (unbroken) magic weapons and armours in their hordes: a) They can use them if they polymorph into humanoid form, and thus break PC weapons, and b) They might kill other humanoids without being able to break their toys, and so keep them, unbroken, in their horde.
6) The DR argument is interesting. But I could simply hold that the WOTC powers that be decided to make it harder for monsters to destroy the PC's favourite toys. Since the PC's like their toys, that could make sense to me. And any creature with /epic damage resistance would still be able to sunder non-epic weapons on my interpretation, since "epic" seems to mean "at least +6" when I read the MM 3.5 entry under Damage Resistance. (I suppose one might argue on similar lines that /magic damage resistance would allow a sundering of +1 weapons (though not +2 ones) since no magic weapon in the core books is less than +1). Well except the monks +0 magical bodies. (And there, I have gone back on topic briefly)
7) I'm glad that your interpretation is easier for you and your game. Can you accept that my interpretation is easier for me and my game?