That's not the same case at all, though. The business owner may "manage" the new employee, but that role is completely different from the role of a manager in the context of this discussion.
So you've said that it doesn't hold true for a 2 person company. At what size of company would you make the organisational shift then? 3, 20, 50? At the point where there is one person between the founder and the lowliest employee?
If your new hire is doing all the creating, then yes, it's your job to make sure their job is as easy as possible and they are as effective as they can be. But this example is a little absurd. Manager wouldn't be the correct term for the founder in your example since they would be filling myriad roles beyond manager, just like the first hire would be filling myriad roles beyond "software engineer".
Let's take the simplest case of this.
You're a one man business, developing software perhaps. You're doing well, you're successful and you take on someone to help you out.
Are you now their butler? Does that person set your salary?
If not, at what size of organisation does manager-as-butler kick in?