The Caveat
Multiple companies working together on a common standard is fine provided that the standard is available in RAND terms to any and all competing companies not involved in the development process. In other words, two companies cannot collude to produce a technical framework that helps their respective products inter-operate, whilst blocking competitors from inter-operating as easily.
For example, it would be bad if Apple worked with Griffin to develop a protocol which gave Griffin accessories extra capabilities or better connectivity with iPhones/iPods/iPads, etc and that protocol was withheld from Griffin's competitors.
RAND = Reasonable and Non-Discriminatory