There is no kind of legal requirement for a business to purchase a business plan versus multiple individual plans, so long as they adhere to license use requirements. Business plans include features which hopefully justify the higher price point, and are typically "a better fit" for most business customers.
The sales agent in post 8 above for B-ecky was wrong. Based on the case history it looks like they downgraded from team to individual because an individual membership suited their needs better. Sean_tiburon's post about their account being upgraded to a team without permissions is not acceptable and looks like it was remedied after his post here. They too were downgraded to an individual membership.
There are features built into the software which can detect if the software usage may be violating the licensing terms. The terms stipulate one user on two computers per individual license. In some cases Adobe has reached out to customers directly when it was unclear how they were using the software and whether they were in compliance with the licensing terms.
Hope that helps,
- Dave