Given the fact that many newspapers seem headed toward nonprofit status anyway, it's perhaps not surprising that someone would try to make it official. Legislation introduced this week by Sen. Ben Cardin of Maryland would enable newspapers to establish themselves as tax-exempt nonprofits and qualify for significant expense savings courtesy of Uncle Sam. Under the Cardin measure, they wouldn't have to pay income taxes on income derived from advertising sales. That's a big difference from existing IRS regulations, which customarily extract federal income taxes on advertising revenue derived by nonprofits. (There are a number of exceptions to this, including one……