QUOTE - "So if a company decides later to change it's mind about how it defines personal vs. enterprise, I'll be forced to either pony up for an enterprise license or go out of business."

Not if it's a perpetual licence you go for, reason being, they would have to define both "Personal" and "Enterprise" within the licence agreement of the perpetual licence. They cannot charge you for a perpetual licence, then later change the licence you agreed to pay money for. If that were allowed, the licensor would be able make any additions they like, and the licensee would have to abide by it.

What you describe is one of the problems subscribers face, because a monthly renewing subscription is only valid for a month, therefore the licensor gets to change the licence agreement every month, or whenever an updated version of the software comes out, whichever is the soonest. With a perpetual licence, though, providing you hang onto the original version of the software which has the licence you agreed to attached to it, they cannot change it, because whenever you install the software, it is that original licence you agree to when you install it, not something else.

I'm no expert, so my post has no guarantee of being correct and I make no claims of it being so. But if the thing you are fearing was valid, that would surely mean that no licence is worth a damn. The whole idea of a licence is that the licensor dictates the conditions, and the licensee only agrees to those conditions and lays down the cash, if the licensee is happy with them.