Then these nice little things called "anti-trust laws" would help out.
And where did you make the assumption that it would happen to stereos? How did you assume that the stereos would have no other ports besides the iPod dock? They also need connectivity with TVs and CD players (because people still use them) and, as you said, the iPod dock is patented!
And I might point out that the iPod dock is not meant for simply transferring sound. It's a 30-pin connector that allows remote control through the dock, information transfer, and so on. Not suited for a stereo system.
Considering that most computer speakers nowadays use the same standard jack, and that standard jack is used by nearly every mp3 and CD player (even the iPod!), I doubt it. Things don't change that fast.