No shadow pruning with system cron enabled

I may just be confused, so hopefully somebody can clarify this for me before I start writing code.

In prune_shadow_topics.php, a comment reads, "This cron task will not run when system cron is utilised, as in such cases prune_all_forums task would run instead." However, that file only prunes old topics, not shadow topics, and I can't find any tasks that deal with shadow topics besides prune_shadow_topics. Were shadow topics just forgotten for cron?