Apparently, leaving the "start w/ delta powers' box unchecked doesn't keep you from using Delta Mode anywhere. Sure, you cannot place delta blocks anywhere you'd like, but you can still actually enter the Delta Mode regardless (it doesn't make sense to be able to enter it when you can't use it).
Before Null Space, you could only enter Delta Mode when close enough to working Delta Orbs, and, correct me if I'm horribly wrong, wasn't that the intention?