IOC is still a way off - fact.
The USMC is not claiming the stand up at Yuma as IOC, just the start of the process. Even the General in his speech said that they would be taking things slowly.
The aircraft still has a lot to do in testing, with 2013 being planned to be the busiest year, but these aircraft at Yuma are not 'test aircraft', they are not instrumented and have all the mission systems fitted.
Your perception of F-35 development can be coloured by what you compare it against. Compare the timescales for development and the air to air and air to ground capability at IOC against Typhoon and F-35 comes out very well. Its then a question whether the capability is worth the cost...