Anyone know how much a 750Kbps international pipe costs? That's what you need to get your 75GB quota. I can see how it would get over subscribed rather quickly.
About US$2500/year - based on the smallest (155Mb/s) link SCC provide costing US$500000/year. Allow for it being used 8 hours/day and the annual cost is US$833 which equates to NZ$110/month. On that figure alone Xnet's torrent plan is unsustainable if the bandwidth is used to the detriment of profitable customers.
You also need to remember that when an ISP signs up for bandwidth the costs at that time are in perpetuity so the actual costs to most ISPs will be significantly higher than those stated above.
As a comparison I have a quote for a trans-Tasman 2Mb/s link on my desk at the moment - it's around NZ$4000/month before we start haggling.
 Cost is taken from http://www.stuff.co.nz/4560779a28.html