By binary search I'm assuming you mean via the "Revision history search" tool that can be found in the history page right? Yeah there are a bunch of cases where

By binary search I'm assuming you mean via the "Revision history search" tool that can be found in the history page right? Yeah there are a bunch of cases where it doesn't work so well, especially if the change happened hundreds of revisions ago, but like you said you can always resort to looking at individual diffs. Regardless, someone can be held accountable for the edits, it's just a matter of having to do more work because of the multi-contributor nature of Wikipedia. And in 90% of the cases, the offending statement is the last edit made; people and bots are usually really good at watching pages and recent changes for vandalism.