Yes, and this is intentional: Think of them as "soft" dependencies that have to be explicitly defined.
If I had added them as a dependencies, the caveat would be that too many extra modules would be loaded, occasionally making the case of combining certain applications even more difficult.

So, the builddependencies are there only for one purpose:
* ensure that when biodeps is being installed, a basic substrate of tools of defined-versions is there to be reused