Reflection: "Learning is on its best as a by-product"

I notice
that the most popular learning tools do not have learning as their primary goal
and I suspect
that slashing formal training budgets doesn't reflect on the bottom line, at least not in the short run
and when I
ask people about their most memorable learning moment, it's usually and experience during real work.

Hence my reflection:
"Learning is on its best as a by-product"
(you can quote me on that)

If that is so, then
how do we design for a by-product? or do we leave it to chance?
do you need a training department and training professionals to do so?
how do you measure the impact of a by-product?

What are your thoughts?