The T18 Easy - Bare Tool runs $199 USD.
The T18 Proper - Bare Tool runs $299 USD, and includes a keyless chuck as well as the Centrotec chuck and Centrotec Bit holder, which retail separately for $70 USD (plus a P2 bit for $1).
So, really, they DO sell the T18 Proper with a keyless chuck, for only $29 USD more than the T18 Easy, but you have to get the CT kit with it).
The T 18+3 also has the registration guide on the front to hold the other chucks in whatever position you want/need them.
As some have said on here and in various other threads, it's a gateway dru--, I mean, tool to get you into the Festool family/system. It's made to somewhat compete with similar offerings from the megabrands.
Honestly, I think it's also similar to selling rails with the TS and HK saws; by offering/forcing CentroTec (itself a swappable system) and at least one more chuck in every variant of the T18+3, it reinforces the idea that the drill is made to swap chucks. If it was sold in a variant with a single chuck, the swappable chucks (or "chuckability") wouldn't be as obvious of a value-add compared to the other offerings on the market. And the T 18 Easy is there to whet your appetite, as Sedge seemed to indicate in his T18 Easy intro/demo Festool Live video.