Never said the transfer value equates to the contract payout figure, but if there was any reason to believe Cesc would exercise that option then I find it unlikely that Barca came up with a figure that just happens to coincide with the same amount.
Wouldn't be taxed at 50% either, although that would be something that would push it to a higher amount. Barca may reflect that in the contract they offer Cesc.
Why wouldn't it be taxed at 50%? Anyway, whilst I believe that Barcelona are unpleasant and slimy enough people to try and push that kind of pay out through, from all reports Fabregas, whilst he would like to go isn't going to force a transfer through that would leave Arsenal at a disadvantage.