Denny,
the problem isn't having the top portion of the seat rip free from the base, at least not the way you're thinking.
Go out to the airport, and take a close look at the way that seat is held in place on the seat base. The only thing that is holding that seat from moving fore and aft is that tiny little rod that drops into a hole to "lock" the seat in place.
So, if you encounter a serious deceleration, with the seat belts attached to the seat, all that's stopping you from sliding right under that instrument panel is that tiny little rod that "locks" the seat in place. Considering the forces involved it's not surprising that little rod isn't up to the job.
If, on the other hand, you've moved the seat belt attach points to the floor, your body is connected to major structure, even though the seat isn't.
Its an important safety mod, in my opinion.
MTV