I'm thinking that since DLP isn't that big (yet), it basically isn't need for any bigger system.
Everything is so close, that it probably would take more time to board a for example a monorail, rather than walk or take the bus. I've heard people over at wdwmagic.com talking about monorails, in regards to expanding the existing one at WDW, and monorail are apparently so expensive, that it is not gonna happen, even at WDW.
When DLP gets more parks, then I can see that they maybe need it.