No, it's got nothing to do with not being able to read the small print, it's to do with them attempting to twist the meaning of the English language using small print.
The dictionary definition of Unlimited, is...
1. not limited; unrestricted; unconfined: unlimited trade.
2. boundless; infinite; vast: the unlimited skies.
3. without any qualification or exception; unconditional.
How can they possibly claim it is 'unlimited' when it is subject to an AUP which contains terms limiting the amount you can use the service?
Examples? Well they really aren't hard to find. I've just checked two of the biggest ISPs in the UK, and both of them use this tactic for services that they offer.
Neither Ofcom or the Advertising Standards Authority has ever taken action against an ISP on the grounds of unlimited broadband advertising, and I think it's time that ISPs were more upfront about this, as it is misleading customers that believe 'Unlimited' should mean 'Unlimited'.