Is this the desired/typical setup for directories after 4.7?
Yes it appears to simply be using $civicrm_root (from the civicrm.settings.php) to look for these dirs! So as long as you have them in the usual places - this will work. 

If you have a dir in a slightly different place or if you give it a different name - then you have to continue to be more specific [either specify exact path or construct it with the path variables]. I must do that for our projects for which we typically name and put the /extensions dir in a different place.