"Once upon a time", the law said 10 years
for electrical/electronic parts.

Urban legend for the most part. California had a
similar law at one time (7 years IIRC), but it was
unenforceable.

Not what I was told, including by my Sony contact -- the head of the parts
department.

Such laws are eminently enforceable. It's just a matter of whether the law
wants to get involved. Dragging companies into court for a relatively small
social benefit might not seem a good use of time to prosecutors.

The real problem is that technology changes so rapidly that manufacturers
have little practical justification for keeping service parts. But the idea
of tossing something because it can't be fixed is fundamentally anti-green.
I expect expensive products to be fixable.