Yea... thats not really correct.
While it is true that some connectors are designed and exclusive to a mfg. Most general, non-application specific connectors are picked out by engineers from a catalog and then are priced out. They are not exlusive and it is very common to find connector series that are on GM, Ford, and Chrysler vehicles.
Say GM has a proprietary emmisions leak detection unit, it is likely that may need a conenctor that will have to fit a bunch of dfferent requiremnets. So to save everyone the hassel of finding a connector that will work and making that fit thier design, they just go ahead and design one. That connector would not be able to be purchased.
So, now whose logo is this ???????????????????
Aside note: There is an easy way to tell if the conenctor is proprietary. NONE of the conenctors I am using have any GM, Ford, or DC logo on them. However I can find connectors in vehicles that do. I am fairly certain these are non-exclusive.