"Gooning it" is how it goes if the PCs can knock it prone consistently. Proning completely wrecks dragons that are supposed to rely on mobility, because it keeps them from flying. The PCs then pig-pile and smash it to bits with CA to boot. Even if it's willing to eat a bunch of OAs to escape after standing up (and possibly having to spend a precious Standard Action for a mere move), if the party has a Fighter or somebody else that can stop it, it's still not going anywhere. I've seen fights against a blue dragon twice, and both times it was totally crippled, first by my Runepriest using an at-will Immobilize, and the second time by repeated proning.
That's why you design the encounter effectively. There's more to dragons than 'PCs have abilities, let's have a fight!'.
In the case of the blue dragon, they will never purposefully close in to the PCs if they can help it. So how do you create an encounter that plays to the Blue Dragon's strengths?
Well, at young, the dragon's pretty dull, but at adult, the dragon has tricks that make you think twice about a constant 'prone you' barrage. At adult, the blue dragon's standard attack includes a push. That's definately a way to get the fighter off him.
More importantly tho... at Elder and ancient... go ahead. Everyone comes in close. The dragon doesn't care; he has a close AoE stun that deals damage that he can use at-will.
Not to mention, a blue dragon's breath doesn't trigger attacks of opportunity--it doesn't even have an attack type!
But then again, what is a blue dragon doing on the ground if it can help it? With fly 10 hover, it's attacking a party from above, and doing so with devilish glee. Blue dragons are actually a TPW against a melee-heavy group. Once a party gets it down to the ground, yes, it should be a problem for the dragon, but getting it to the ground should be a pain in the ass. Doable, challenging, and THAT is the real game of that encounter.
I think that a mistake a lot of DMs make with dragons is the 'Well, he needs to attack this round so...' and think that their standard actions need to be attacks for them to be effective. That's far from the truth. While red and white dragons should be going toe to toe, black, blue, and green dragons are better suited to hit and run tactics. They have abilities to get them OUT of trouble, and punish those that try to put them into trouble. Most of the time, these 'easy' encounters are because the dragon isn't being used according to its role.