If the NSA's Prism is no big deal, why was Yahoo in court fighting it?

Top lawyers for Yahoo argued in a secret court in Washington that the company should not be forced to assist the government in spying on "certain foreign users, without a warrant," which Yahoo had refused on the grounds that such broad requests were unconstitutional."The judges disagreed. That left Yahoo two choices: Hand over the data or break the law. So Yahoo became part of the National Security Agency's secret Internet surveillance program, Prism, according to leaked N.S.A. documents, as did seven other Internet companies." [NYT]