Thank You Sir!
This isn't a ''maybe" or "sometimes", it is something that I believe must happen with all speakers. I have had this experience with almost all of the 20 sets that I have owned over the years. I think I picked up the habit from advice that I read in one of the Brit mags many years ago.
I had to chuckle a bit when you said that you had never encountered loose woofer screws, because they are the drivers that become loose most frequently due ti the heavy movement and vibration!
This isn't a silly tweak, it's part or regular system maintenance. Of course, you need to use common sense and don't over tighten.