MacBook :: Swollen Battery, Still In Applecare, That Apple Won't Replace

I've got a Macbook Unibody which is still covered under AppleCare, and I discovered that the battery has swollen and became slightly bigger, enough for the battery cover not to close properly. The battery has only 200 cycles and is still on 84% capacity, and I have AppleCare until November 2011, so I thought it was a battery defect and took it to my local Apple reseller. (no Apple stores here yet )

So, after two days I was told that they had checked my Macbook and found the cause for the battery to swell up: there was a lot of dust on what seems the output of the processor disippator (a place I wouldn't be able to reach myself to clean, as I would have to disassemble it), and that dust caused the processor to become hotter (even though I hadn't noticed it) and that too much heat caused the battery to swell up.

But the funny thing is: Apple won't authorize the battery replacement, because they say it is not a battery defect, as it was caused by the processor heating because of the dust that got there by "normal usage" and I couldn't clean by myself. They told me I should have got there by the time I noticed my laptop becoming hotter than before so they could have cleaned it, but now it was just too late.

So I was left with the laptop and the swollen battery again, after I refused for them to charge me for the battery a little bit more than the price that I could get it from the online Apple Store.

any experience with swollen after normal usage batteries? Will the battery swell up more if I keep using it? Do you have any idea on how to convince Apple to give me a new battery? (after all, batteries aren't supposed to swell up, aren't they?)