Motorola changed hands and direction after the Google purchase, and, with everything that has changed in the Droids, I think it's clear that they were going for a couple of things: close to stock Android, and anything that was added was made to be as simple to use as possible. Smart Actions was developed by the "old" Motorola, a company that basically failed and had to be sold.
Smart actions can be replicated by power users with great third party apps, but for less technical users, Assist, Touchless Controls, etc., are easy to set up and do what they do simply and well.