Avoid Festo Presumptions With a Letter to the File?

Professor Douglas Lichtman at the University of Chicago writes with a question about patent prosecution:

Why haven’t patent prosecutors begun to aggressively document the purpose behind their claim language changes, for example by writing letters to the file making clear a precise and narrow construction of the change. The argument to do so is that such documents would rebut the broad Festo presumptions that right now threaten to construe every change broadly. And it would be cheap to do.

I am not advocating anything misleading. But often changes are made for a very specific reason, and claim language changes (like claim language itself) can be imprecise. So why not clearly document the precise change the examiner requested, making clear what you meant to sacrifice and protecting the rest from Festo?

Please e-mail your comments to me or Professor Lichtman.

UPDATE: The real question is why patent attorneys do not precisely define in their office action response what you intend to give up in an amendment. For example, why not say “of course, my purpose here is only to exclude red wheels, leaving fully intact everything else that might have been included in the original claim language.”