The nonreporting issue is probably related to the difficulty of recordkeeping for opening/closing transactions for writers of contracts and the expiration of the contracts.
Pages 56 and 57 explain the details of tax reporting for investors - http://www.irs.gov/pub/irs-pdf/p550.pdf
I can't find any regulation that states the reason that these transactions are nonreportable. The IRS 1099-B instructions do not address these types of transactions other than the broker may (but is not required to) report the exercise of call options.
Page B-2 - http://www.irs.gov/pub/irs-pdf/i1099b_07.pdf