This is common, or at least, I've definitely had my parents do this for me, and I know my friends have too.
The logic is as follows: I need to be up early, my parents always get up early, and my alarm almost always works. If I have both to wake me up, there's a good chance I won't accidentally sleep in.
The logic is as follows: I need to be up early, my parents always get up early, and my alarm almost always works. If I have both to wake me up, there's a good chance I won't accidentally sleep in.