Well, they have a disable switch in the Technical Preview operating system such that it won't run past the date they set, and since it has to be in touch with the Mothership over the internet, you can't just "set the clock back" on your own computer and fool it.
The ISO itself doesn't get disabled, per se, you'll always be able to burn a DVD from it, install from it, etc. but the resulting installation of the OS won't run past that disable date.
So that’s how that works