[AtlUmpSteve]

The difference, in my opinion, is that the ball sitting on home plate is in front of the BR; she should be able (and therefore required) to avoid interfering with it. Any ball in front of you (well, almost any) should be avoidable.

But a thrown ball is most often from a blind side; and the onus is based on the runner doing something specific and active to interfere, as opposed to failing to take reasonable caution to not interfere.