The problem isn't a lack of a guarantee. The problem is _never_ getting the service as advertised.

If I buy a 50 Mbps plan, and I get 50 Mbps 60% of the time and between 20-30 Mbps 40% of the time, I could live with that.

My problem is that has never been my experience with major cable providers.

I pay for a 50 Mbps plan and get 20-30 Mbps 50% of the time and 10-20 Mbps 50% of the time. That's not simply a lack of a guarantee. That's a complete failure to provide the service that was advertised.

Again (as above) I feel I need to speak up that we have a bigCableCo connection (Charter) that delivers 1.2x the sold throughput. From talking to the local guys there, they have a policy to over-provision connections by about 10% so they can be sure a speed test will deliver what the customer paid for.

When I ran an ISP it was common for customers to run a speed test, see a speed less than they had paid for, and immediately call us. Often the reason was their router or their WiFi, or some flakyness in the speed test site, but sometimes it was our network. We always investigated and resolved the problem to restore their expected speed.

This being the case, I find it quite hard to believe that there are ISPs who as a matter of course just don't ever deliver the advertised speed. They would be receiving constant calls from disgruntled customers, which surely would cost them more to answer than it would cost to fix the network??

You can easily (through shoddy, cheap outsourcing body shops in India, Phillipines, etc.) get support costs low enough that just taking the calls is cheaper than fixing things, at least until the end of the financial quarter, and that's what really matters to management. I say this from experience in the web hosting industry, but I don't see any reason it wouldn't apply to ISPs.

No the problem is unethical companies that sell 6mb dsl from a DSLAM fed by 2x t1s, or that refuse to upgrade their peering links because they want their peers to pay them too.