Wrong. Something is out of balance to get a speed wobble. A harmonic does not begin unless something is seriously out of balance or there is is something that is allowing a very major amount of flex that should not be there to begin with.
You need to spend some time engineering a chassis and learn about how wheel balance and weight can impact a chassis.
Ok, so something on the bike is not in perfect balance. That doens't mean the wheel bearings are shot, or the headset is out of adjustment. I seriously doubt everything is in peferct balance on any bike.
I've expereinced the wobbles on every nike I've ever owned, except for my current CF TCR Team Advanced.
Some were more prone to it than others, and it appears to be related to frame stiffness. Some wobbled in the 30's. Some it took in the 50's, and none of them wobbled to the point it wasn't correctable.
And a number of those bikes were top end racing bikes for the day, with handbuilt frames, and top end groups from Campy or Shimano.
And it happened when the bikes were relatively new, so not enough time to wear out the bearings.