sorry but 3 years is ridicolous and your comment is also insulting to the millions who dont own their home.
Many isps change hugely over a 3 year period and as stated earlier a 18 month contract already requires a lot of thinking to commit to never mind 3 years.
Even with homeowners, they cant really see the future, issues may happen that leads to them moving home.
I take your point that 36 months is not suitable for people renting (who would also be unlikely to want to pay the upfront outlay given it is not an investment in their home). As I mentioned though, I would only consider a 36 month contract as a home owner who did not intend to move - it's hardly an insulting comment to anyone!
RobertoS mentioned £100 per month. Where does this number come from? During the 3yr contract term, AAISP charge £20 + the number of units you use (around £5 per month for the amount I use it). People's circumstances change but other broadband packages are not much cheaper than this so it's not an excessive commitment if you think you'll need broadband irrespective of your circumstances. AAISP's monthly price increases after the initial 3yr term but you're free to move at that point if someone is better.
The fact that ISPs change over 3 years is very fair - there is clearly a risk here so you would need to choose your ISP carefully.
It's clearly a niche product given the upfront cost is not affordable to everyone. However, it is an option available which is better than not having any choice at all isn't it? The install cost is a significant barrier to people but if you can afford and justify this, the 36 month contract seems less of an issue to me on a relative basis.