ISPs (I work for one) dislike traffic, which heavily saturate channels. Total uplink capacity is comparable with total customer demand at peak hours. So, ISPs have to distinct between immediate (VoIP, gaming, SSH), normal priority (web browsing, email) and bulk (BitTorrent et al) cases. Although, throttling to pre-defined per-customer value seem like stupid idea, but putting them into different buckets is a must.
ISPs also dislike high-PPS low-packet-size (significantly lower than MTU) UDP traffic of uTorrent's uTP protocol, because it quite negatively affects the network hardware.
And, most important — ISPs, in fact, love P2P traffic when it happens between their peers, because such traffic does not consume uplink channels. When it's legally possible — they endorse it (for example, by setting up gaming servers or introducing locally-hosted software-update mirrors), when it's a gray waters of file sharing — they just don't stick their nose in other's business (unless law enforcement requests them so). Of course that's unless they want to make customers dissatisfied their service as network connectivity providers.
This is presumably what was specifically causing the WoW throttling from the article.
>>"We recently introduced a software modification to solve the problems our customers are experiencing with World of Warcraft. However, there have been recent changes to the game, which has created new problems. A second software modification to address these new issues will not be ready until June."
I'm not 100% sure, but iirc the "recent changes" had to do with WoW changing the TCP ack frequency when running, more than doubling or tripling the total number of packets sent over any given period of play time. They turned this on with a recent patch, but hotfixed it off temporarily because, as you said: "it quite negatively affects the network hardware". People with crappy routers/modems were apparently having problems staying connected.
ISPs also dislike high-PPS low-packet-size (significantly lower than MTU) UDP traffic of uTorrent's uTP protocol, because it quite negatively affects the network hardware.
And, most important — ISPs, in fact, love P2P traffic when it happens between their peers, because such traffic does not consume uplink channels. When it's legally possible — they endorse it (for example, by setting up gaming servers or introducing locally-hosted software-update mirrors), when it's a gray waters of file sharing — they just don't stick their nose in other's business (unless law enforcement requests them so). Of course that's unless they want to make customers dissatisfied their service as network connectivity providers.