Logic is not just a step up from GarageBand, GarageBand is Logic re-skinned, if you use GarageBand and import into Logic, you can see how all the simpler instruments in GarageBand were created by configuring the more complex Logic instruments. Logic is probably integral to GarageBand not just as being the same code base, but as the creative tool in which the GarageBand instruments are designed and prototyped.
