winterbadger | clarification on medical billing

I got a response from Aetna the day after I emailed them, which I have to give them credit for.

Their argument is this:

Office surgical procedures are paid at 80% subject to the $600 calendar year deductible. The office visit copay applies to non-surgical services performed in the doctor's office. The billed amount on this claim is $290 and the contract rate is $141.01 which was applied to your deductible. The provider writes off the $148.99 contractual adjustment. Therefore, since $141.01 went to the deductible you are responsible to pay this amount. You paid $25 already and the provider has credited your account. Their billing of $116 is therefore correct.

I'm not sure that I really understand this; maybe one of my more medically savvy friends can help me out? What do they mean by "contract rate"? I guess what I think I'm hearing is that they have an agreement with the provider that the going rate for this is $141, of which they will pay 80% *once* my deductible (I hadn't realized there was a deductible) is exhausted. The $149 they "pay" only in the sense that the $141 is a discounted rate that the practice offers them; no money actually changes hands. Thus, if I had already used up my deductible, I'd be paying 20% of $141 instead of all of it.

Mant, that's as clear as mud.