the rules on page 66 are not made pointless because a fire spell cannot set things on fire. Again, powers and spells have their own rules... something like lighting a book on fire with a torch does not have actual rules covering it and could be what both the rules on page 66 are meant to be used for as well as those on page 42 that you cited.
The example on p 42 is of a PC pushing an ogre into a brazier of coals for 2d8+5 fire damage.
According to the rules on p 219 of the PHB, though, an improvised weapon does 1d5 untyped damage. So, on your theory of "houseruling", isn't it a "houserule" to have a torch do [fire] damage? Or to have coals from a brazier do 2d8+5 [fire] damage?
Or, to put it another way, I don't know what you think p 42 is for, but I know what I think it (and other stuff, like pp 65-66) are for. As I quoted upthread, p 65 says that "Like characters, objects have hit points and defense scores". That doesn't give me the impression that these rules are primarily for burning papers with torches and knocking down doors with toothpicks. They give me the impression that they're for settting fire to buildings with fireballs and knocking down doors with axes! For me, that's the point of saying "like characters" (which is in turn a synonym, or near enough to, for creatures). The rules are telling me that things that hurt creatures can hurt objects too, subject to the restrictions and guidelines noted on p 66.
Pages 88 through 93 of the DMG have a range of traps with defences and hit points. I don't know how
you imagine the designers envisaged those traps being attacked, but
I think they envisaged that powers would be used!
So again, there are no actual rules for this, it's just whatever rules the DM wants it to be
For some reason I don't understand you seem to think that pp 42, 65 and 66 are not part of the rules. Because they're the rules I'm pointing to. And they are not about "whatever rules the DM wants it to be". They are very clear rules for DCs, damage values and the like, which are to be used to "make it possible for the players to try anything they can imagine" (DMG p 42).
Sure, and Rule Zero means that 3e doesn't really have an issue with grapple rules or caster/fighter disparity.
Rule zero = (not too loosely paraphrased) "It's the GM's game and s/he can do what s/he wants". Pages 43, 65 and 66 of the DMG is 3 pages of charts and guidelines for adjudicating improvised attacks (including against objects).
There are some people who run 4e of nothing but p 42 plus the monster-building charts: these are the mechanical spine of the system. The equivalent from rule zero would be to give a GM a bag of dice and say "Hey, go nuts!". If you think those are much the same thing, you think about RPGing very differently from me. If D&Dnext is being designed on the premise that those are the same thing, I don't think it's the game for me.
These are for actions not covered by the rules... a power/spell etc. is very much covered by its own set of rules and some powers/spells can target objects because it is listed as a target in their mechanical representation... others do not have it listed and thus the logical conclusion would be that is because they don't affect objects.
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"object" is a valid target for some spell/power target lines... isn't it? Why is that if your assumptions hold true?
Because, as I've already mentioned multiple times upthread, a power that has "object" listed as a target can attack a target without the need for GM adjudication of the fictional positioning. Whereas once pp 432, 65 and 66 are in play the GM is expected to adjudicate the fictional positioning: see PHB p 8: "When it’s not clear what ought to happen next, the DM decides how to apply the rules". So when I try to use my fireball to set a ship alight, and it's not clear what ought to happen next, the GM decides how to proceed, drawing upon p 42, pp 65-66, and also the multiple suggestions throughout the DMG to "say yes" to player improvisation.
we are discussing the clarity, or lack of in 4e as far as whether powers/spells/etc. can affect objects or not.
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apparently it was a widespread enough issue that the designers felt it necessary to add the rule to the game in later books, right?
I am not discussing the clarity of 4e's rules on this point. [MENTION=69074]Cyberen[/MENTION] made a comment about editing a bit of a way upthread, and I didn't see anyone disagree.
I am discussing whether or not the rules of 4e, as published in mid-2008, mean that a fireball cannot set things alight. I though that you were asserting this. If you're now simply saying that the editing could have been clearer, I don't disagree.
As to why they made the revision - perhaps they wanted the clarity? Perhaps they felt not enough people had paid attention to pp 65-66? Maybe it was an abundance of caution - after all, it always struck me as obvious that Weapon Focus would only confer a damage bonus for attacks with the [weapon] keyword, and not (for instance) when a weapon was used as an implement, but they issued a clarification on that one too.
contrary to your play preferences a DM can adjudicate that spells don't work on objects and that is also a valid (I would argue a more valid... by the book) interpretation of how spells work.
Rules-valid != good idea. Just follow my golden rule of Rules Interpretation: "If there's two ways to interpret a rule, and one of them sucks, do it the other way."
I'm sure some Basic D&D GMs ruled that, because there were no rules for jumping, the PCs couldn't jump - and when they were pointed to Moldvay's comments in the GM advice chapter, muttered something about "houserulings". Those GMs sucked too!