That's actually not false advertising, you're just applying the term 'unlimited' in a much more broad sense than carriers are.
The plans do only offer unlimited downloads and uploads of data byte amounts without the restriction of overage charges within it's set coverage area. By advertising plan offerings a long with the detailed terms and conditions all internet providers offering 'unlimited' (wireless and landline) meet legal requirements.
Inferring that 'unlimited' should apply to speed wouldn't make sense, as it would be limited based on the technology in use (2G/3G/4G, DSL/Cable/Satellite), bandwidth, location, device used, location of use, and the provider's terms & conditions.
Insinuating that any carrier is advertising unlimited speeds, time, location is ludicrous. Consumers should read the details of any offering's terms and conditions. It's the same with any industry, even restaurant's offering 'all you can eat' are allowed to stop cooking, close after hours, enforce dress/conduct policies even if patrons can still eat and that's also not false advertising.
While you can still download/upload as many bytes as you'd like to without the restrictions of overage charges in the US, you can't use data in the middle of the ocean, in some basements, if your battery is dead, or quicker than the parameters allowed by the network, device or provider.