I consider this argument ridiculous, as the in-car-software controls nowhere near as much of the user experience as the operating system and applications of a personal computer. Today's car builders have their profit margins because of engine design, build quality, exterior design and branding. They don't lose power by outsourcing their software stack. Actually a lot of them already use the same software over their entire model range (f.e. Volkswagen, Ford, BMW all do) and it does not seem to hurt the sales & profits of their top-end models, so the point that software is the crucial buying factor is basically already refuted.
(I think they should rather be afraid of Tesla overtaking them in what actually matters)