They have a 1 month contract period, try find that elsewhere!
A lot of UK ADSL providers are only on 30 day terms, unless you want free routers etc.
ISP's will, undoubtedly, try and find ways to charge more for the services they are offering which have become cheaper and cheaper over the last few years. It's not out of spite, they have genuine issues of capacity.
I'm not a fan of paying for the exact amount of data used, however. Fair-use caps are better, provided you can find one that has a high enough cap at a low enough price. I still prefer unlimited connections, and currently have such connections from Nildram and Eclipse Internet.
Quite an exciting development for users that consume less than a few gigs of data per month is mobile 3G broadband from the likes of Vodafone and T-Mobile. Both offer a USB modem that plugs in to pretty much anything and goes with you anywhere. Draytek has a router that transforms the USB modem into a shareable Internet connection. Currently you'll get up to 1.8mbps from such a link, but upgrades are already under way to make that 3mbps+.
The mobile operators are worthy of a mention here because, for the last few years, they have almost exclusively charged per-byte of data transferred. 'Fair use' caps are a recent evolution that finally allows for mobile data usage without the fear of mega bills.
Customers, generally, don't like the pay-for-what-you-use model. They, generally, like to know they've paid their fees and that they're set in stone. A letter or call from the ISP is fine - a warning wont cost them any money - and even if they will only use a fraction of the fair usage cap in real life it's just knowing that there
is a limit on how much they'll pay. So, I can see a future of ISP's charging different amounts for different levels of usage, but doing so in terms of fair usage caps and not raw data use. A 'limitless ceiling' of charges when there are viruses and wotnot out there ready to saturate your connection without your interaction would just be insane.