Sounds to me like they want to offer a Business level tier. The wording "should not host any type of server" was probably groomed by the legal team. My guess is rather than define what a server is, which is almost impossible, they are covered by that vague terminology.

The important question is to what degree do they enforce it? 0.01%? If so, then no big deal to me. I'm paying a lot more for a lot less with my current ISP. I'd be glad to endure Google's draconion rules.