Yep it's true. There's what they call a transponder in the key, it is interogated by the computer to make sure it's correct before it'll start. It's a scurity thing and a darn good one at that, so nobody can start your Sorento with a key they've just had cut.
Sorento can "learn" new keys but they still have to have the chip in them.
If you hold your old key next to the recut one it will probably work, don't think it actually needs actual contact. So, you could probably stick the old key near the ignition switch and use any keys you like, sort of a bypass, but don't complain if somebody hot wires it and steals it OK !!!
2005 2.5 CRDi Auto Sorento sold
2008 2.0 TDi VW Tiguan :o