They buy less capacity than they promise to provide. I don't think they actually throttle, for example there was one evening in July during the constructions vacations that I got the full bandwidth, was great that one time. If they throttled it would've been ALL the time.
TBH if I only needed 10-15Mbits vMedia would've been fine. Issue is when you pay for more and don't get more. Like the time I wanted to watch the F1 race before bed on a Sunday: Check usenet around 7PM, race is there, 4Gb or so, start the download expecting it to take the usual < 10 minutes, gives me over 2h.
Gah...
Plus it was the first time I ever say Netflix pixelise on the Apple TV4. Broadcasting any twitch was impossible. YouTube took forever to load, imgur too.