Bullhead City, AZ
It's all about the contract
I think it's really down to contract enforcement.
Most ISPs offer "unrestricted" service to residential users, but preclude the operation of "servers". However, ALL applications that provide a bi-directional data exchange are "servers": email "clients", WEB browsers, FTP clients, games - all these can be classified as "servers" if the definition is used literally. What the ISP is actually saying is a "server" is any service or protocol that can generate more traffic than an "average" customer's internet usage should.
The average ISP contract doesn't usually enumerate the protocols or data volumes that constitute "server" use. After all, if I'm uploading a full week's vacation pictures to an ISP-sponsored photo sharing site, am I not loading as much traffic as a bittorrent? Is downloading thousands of SPAM emails an hour to my Outlook Express client considered to be "server" volume? How about 4-5 hours of YouTube every day?
If the contract doesn't explicitly enumerate the protocols restricted or the volume of traffic that constitutes "abuse", then the ISP is "guilty of stupidity". The only way out is to take an action - like RST forging - that is a "grey area" in the contract. It may not be illegal per se, but it's certainly against the principle of the contract.
Of course the ISP could use QoS or other tools to limit the impact of these "servers" - but it would then be violating it's own contract, as the use of QoS is certainly not outlined in any of the contracts I've had. The could also do as DirectWay does, and enforce a "Fair Use" volume limit. Once again, if the "Fair Use" policy isn't part of the contract, then the ISP is at fault for implementing it.
DirectWay explicitly states the limits of "Fair Use" in its contract: you buy more expensive service levels to increase the maximum volume allowed before the "Fair Use" policy kicks in. If you want to run torrents on DirectWay, expect them to take a LONG time, as you'll consistently hit your "Fair Use" limit, drop speed for an hour, then go and hit it again. No worries here: you knew the rules when you signed up, and that's what you play by.
The only reason that the major ISPs haven't implemented this in their contracts yet is to make their service look competitive to the average consumer and gamers. Seeing a QoS or "Fair Use" limit in the contract, or hearing about it from friends or in the news would get the average Joe looking for a new "unrestricted" ISP - even through neither restriction would ever impact them. It's the PERCEPTION that they're being "restricted" that sells - and surely another ISP or telco or cableco would jump all over this in a competitive market.
Hopefully this will take a turn for the better with the stink over the RST throttling getting mainstream news play, and ISPs WILL start including QoS and "Fair Use" restrictions in their contracts.
On the other hand I'd LOVE to see the DoJ bitch-slap the major ISPs with a Consumer Protection lawsuit over failing to be truthful in the interpretation of contract terms and failing to "educate" the customer on what they actually purchased - in plain language.