It's the head bearings......ask almost anyone who has put a lot of miles on a VTX 1300 or a Goldwing........most riders of those bikes replace the stock ball bearings with roller bearings and the problem goes away and the wear on the front tire doesn't effect it. Both of those bikes have the exact problems you describe.
Nah....it's the tires.
It's Yamaha's secret, patented way of telling you it's time to change the front rubber.
Brand new Azaro...no wobble. 6800 mile Azaro, decel shake @ 50mph.
Brand new Storm...no wobble. 10,500 mile Storm, decel shake @ 50mph.
2nd brand new Storm...no wobble. 12,300 mile Storm, decel shake @ 50mph.
Brand new PR2...no wobble. 6,000 mile PR2...not worn enough yet. No wobble.
I've never touched my steering head bearings. Bad tires = wobble. Good tires = no wobble.
If it was steering head bearings, the bike would always wobble. It doesn't. So it isn't.
Ball bearings > roller bearings doesn't get rid of the problem. It simply masks it, like a poor-man's steering dampener.
The problem is, masking a worn-out or crappy tire is asking for REAL trouble.