That's certainly a problem about salesmen taking their clients and other relationships with them. For small sales-only companies anyway, where the company doesn't provide much infrastructure beyond a desk and a phone. But in those cases, maybe the company really is a bit worthless and it's the salesmen that created the value mostly independently and should be able to keep it.

Don't forget that not only do companies lose their "IP" with outgoing workers, but they also get more free with incoming ones. Perhaps it balances out but with a net positive effect since effective skills get spread around the industry instead of being locked up whereever they were discovered.

I think this is part of a bigger argument about how much IP protection is enough to encourage innovation but not so much that it stifles the market. You seem to be advocating protecting every last little bit of knowledge but perhaps that's stifling for the economy overall even if it is more fair for individual members.