If they were you could drop in any effect you wanted not only that Arturia decided to build in.
For the Modular it comes IMHO natural as the orginal has I/O connectors everywhere. I don't know if it has been possible to run a signal from the OSC without any amp into a stomp-box but we could imagine we use a pre-amp for that purpose. And perhaps some nifty engineered solded together stuff that Moog's company didn't sold directly. Anyway, Arturia has added so many things that weren't possible with the original so why bother.
Certainly possible it would have been for the B3. The simulation actually comes with a set of virtual stomp-boxes that real organ players would have used. Too bad you cannot add your own set of virtual devices to the B3.
Masi