Like MarkT said, rims have changed over the years, I had a WR250R that doesn't use beadlocks and never ripped a valve stem. Tried taking them out of my '72 CT2 175 with a fraction of the horsepower and ripped off a few valve stems, especially in wet conditions with the chrome rims, it's bad.

I raced 'mx' on a MK8 Bultaco Pursang in "75 which had original Rim Pins instead of tire clamps [security bolts]. Was never a problem until i got a puncture on the last lap uphill & it sat there ripping the tyre bead to bits haha. Wasn't impressed.