The point of a diff. brace on the affected Explorers is to prevent failure in the first place. If you are worried, you could either get permission from your dealer or remove it if something happens since they are easy bolt-on items. I put mine on my 25' within a day or two of buying the vehicle. I will deal with the dealer if / when an issue occurs but I am doing my better part by trying to prevent an issue all together during, or after, the warranty expires.
Furthermore, if you want to get down and dirty, Ford would need to prove, not just "say" the brace caused the failure in the first place before denying a warranty claim.
To each is their own but the failures related to the newer single bolt set-up became a huge issue and resulted in a recall. The original 2-bolt design did not. Ford's fix to the issue and sticking to the single bolt set-up is laughable.