Well
before, it was multi-verse.
There were portals that took you to the creative world (and vice-versa) the same way the Nether is generated.
I know, but the survival side alone is what I'm asking.
And also, since we're on the subject, there is an exploit where if you leave the Creative world with items in your slots, you'll enter the Survival world with them.
Though I don't believe it really matters due to the fact Survival really isn't a big deal to most, I thought I'd bring it up in case you weren't aware of it.