As Jbforum and neowolfwitch note, there's a problem with legal terminology here, and it's difficult to define just what Google and almost every other residential ISP wants to prohibit.
As examples, it seems obvious that Google and other ISPs are fine with someone running a Minecraft server, while they're not fine with someone running a webserver that gets 100,000 visitors a day and saturates the connection most of the time.
But the problem here from the ISP perspective is one of bandwidth usage, not content neutrality, and trying to frame it in terms of content causes problems. As people point out, almost everyone is running some sort of server at this point, and there's a wide range of what can be considered a server.
Unfortunately, simply banning "servers," and using it as an excuse to kick people with consistent and extremely high bandwidth usage off your network, probably makes far more sense from a marketing perspective than having to have some sort of direct limitations on usage, likely involving metering, caps, or slower speeds. I don't think an uncapped symmetric 1 Gbps connection for anywhere near the prices Google is offering is reasonable if customers can use the lines for large production servers.