Money-market funds (MMFs) may have fought off tighter rules for now, but regulators have a variety of options if they opt to continue the fight. Regardless of regulatory efforts, the age of money funds as havens for corporate cash may have passed.

Securities and Exchange Commission Chairman Mary Schapiro called off the commission's vote on money fund reforms when it became clear there weren't enough votes to pass it. The proposal aimed to stymie runs on money funds by requiring them to establish capital buffers and let their share prices float instead of being fixed at $1 per share.    

Even if the SEC had voted in favor of the proposal, companies' use of money funds appears to be waning. Ben Campbell, president and CEO of Capital Advisors Group, notes that the SEC's Rule 2a-7 effectively reduces the weighted average maturity of money fund investments to 60 days, and in practice funds' maturities are now under 50. That's down from an average of 90 days prior to the financial crisis and 120 days before 1991, according to Campbell.