A rat will run to a bit of peanut butter on a trap and get killed by a swinging bar. They're morons.
A dragon is a centuries old beast of cunning, that knows to avoid obvious traps, and when to fly away and when to attack via an ambush. It knows to take advantage of the terrain, it's abilities, and to lure other people into a trap.
None of that is in the statblock beyond the Intelligence score.
I think it can benefit the game when it is, in fact, expressed somewhere in the mechanics outside the intelligence score.
For instance, classic D&D had rules for evasion and pursuit which include the chance that animals, or low-intelligence creatures (eg ogres) would be distracted by offerings of food. This can also be used to adjudicate the prospect that a rat will enter a trap.
4e had rules that could occupy a similar functional space, though based on a very different mechanical structure, with its skill challenges.
But in any event, Mr Mind (from the old Captain Marvel comics - head of the Monster Society of Evil, and a hyper-intelligent worm) also knows how to avoid traps, to lure others into traps, etc. But I think that a dragon should have a stat block that somehow differentiates it from Mr Mind.
But an adult dragon shouldn't just charge at the party like a Tyrannosaurus Rex
Why not? That's more-or-less what Smaug did, and he was able to conquer one of the great dwarfholds of the age.
If the fiction tells me that a dragon defeated a dwarven army, the statblock should somehow express this. The GM "roleplaying" the monster is not, in my view, a substitute for that. (Unlike [MENTION=58416]Johnny3D3D[/MENTION] I have been fortunate not to have the issues he did with 4e - perhaps because I have been using MM3 numbers since late heroic tier, or perhaps just through seer luck - but I agree with him that, if in fact the mechanics aren't delivering results that correspond to the notional fiction, then something has gone wrong and one or the other clearly has to give.)
EDIT: In my 4e game I have run two dragon encounters. The first was at 4th level (or thereabouts), against a young black dragon from the MM. Despite the criticism I've seen of MM black dragons, this encounter went very well - the PCs got some archery off as the dragon approached, and then had to engage it in melee and cope with its darkness cloud (which the PC wizard was dispelling by channelling arcane power through a statute of the Summer Queen that the PCs had in their possession - mechanically, this was p 42).
The second was at 26th level, and involved an ancient white dragon and ancient blizzard dragon, the former being ridden by a frost giant chieftain. This was an aerial assualt on the PCs' Thundercloud Tower, which they were flying down the Glacial Rift of the Frost Giant Jarl. Given it was only a 27th level encounter it was a pretty close thing, and (in my view, at least) satisfyingly epic, ending with the PC fighter leaping onto the back of the dragon, pinning its wings and riding it to the ground as it crashed. From the point of view of fiction vs mechanics, I can easily believe that a dragon which was so hard for a group of demigods et al to defeat would be a fearsome terror to ordinary folk, and a suitable pet/companion for a powerful frost giant chieftain in league with Lolth and the Prince of Frost.