You're mistaken. It's completely different. While all file syncing tools will let the NSA intercept and mess with your data, a web client like 1Password could trivially be modified to intercept a password or decrypt in place and send data back to the mothership in the clear. Dropbox can't force 1Password to modify its binary.
True, Dropbox is better in that regard. Still, the advantage of SyncThing is that an attacker would have to break TLS to even get to the point of entering the master password.
