Roger, that may be it, and anecdotal stuff dies hard, but the presentation was confusing (at least to me!).
The fact is that a non FF forend may accelerate that but from our experience promiscuous full auto fire will grossly accelerate wear on the bolt. Again, we see the lugs crack at 10-14K rds, at about which time the throat is sufficiently eroded to replace the upper anyway.
Compare this with the M16A2, which- in the hands of the average Marine Grunt, will see 500rds per year down range.
They will of course last forever.