The stringent provisions for the 2009 mission probably have their roots in some ill-feelings engendered in the science community by the way that MSSS handled release of MGS/MOC data. The buzz is that a lot of professionals felt that Malin & Co. held on to the data a bit too tightly, delaying release until the last possible (contractual) moment, to give themselves first shot at making discoveries. Indeed, while the contract called for no more than a six-month delay, MSSS interpreted it as six months after each six-month observation period, so that the total delay was more like a year for each release.

Six months is still considered a reasonable amount of time to prepare data for release (MSSS was perceived to have pushed the definitional envelope a bit too far), and that's the standard for all missions.

Took me a long time to find, but there is an official plan for releasing MER data, the MER Archive Generation, Validation and Transfer Plan (PDF). Bottom line is still the customary six months delay releasing raw data to the Planetary Data System for public release: August 3, 2004 for Spirit, August 24 for Op for the first 30 sols of data, with release every 60 days of subsequent 30 sols' worth of data (yeah, huh? that's what it says....). I think the release of smaller quantities of data more often is probably the strongest hint that the system's been reformed and tightened up.