This passage is about a player directly attacking an object... Not about whether a fireball used in an attack against creatures in a room full of combustibles while attacking a creature will ignite said combustibles. You're stretching so far now it's not even funny.
Nope. This rule has been clarified/updated - to make its intent more clear. The fireball doesn't specifically target
a creature, or even a number of them, it targets
creatures in the burst. There is an important distinction there. In this case, creatures may or may not include objects subject to fire damage. Nothing has really changed here.
The thing is any way you slice it, it's still a DM call on whether my fireball can ignite papers or melt metal... so it is not an inherent property of the fireball power itself as it has been for the spells of previous editions.
No it's not an inherent property of the fireball, it's an inherent property of attacks with the Fire keyword, IF the DM decides that it is relevant. There are any number of reasons why a DM may choose not to have things catch fire.
Really? This is the card you're trying to pull now... that I haven't read the 4e books. I'm not even going to respond to this.
There are clearly some people in this thread, arguing on the same points as you who haven't.
And this can happen just as easily in 4e... A player that doesn't want to ignite a room on fire can just as easily cite that the rules state creatures. Now the DM can, just like in every edition, rule whatever he wants... but I don't see how 4e in any way stops the problem you've stated above.
A player can cite that all day long, but it doesn't make it
right. For the
6th time... Rules Compendium page 107. The game has specifically put that in the DM's hands. Like before, but with even more room to adjudicate when the rules lawyers try to object.
This isn't what we're discussing though. Mark CMG hit it on the head, if I throw a fireball at a creature (and I'm not targeting an object specifically) into a small study full of books and parchments in 4e does it or does it not ignite things in the room? According to the rules of the powers it doesn't and according to the passage in the DMG it can target an object if the player wants to but whether it does or doesn't ignite combustibles not specifically targeted by the PC is not addressed.
Except that misses the point. You don't target a fireball at a specific creature - ever. It is an Area burst 3 - its target line affects "All Creatures in the burst," which, naturally includes any objects, if the DM decides they want to deal with that (some groups/DMs may choose not to - and there's nothing necessarily wrong with that). But you know that, because you read and understand the rules we're talking about here.