On a few Japanese bikes I have had, the toolkit contains one spanner of each A/F size. And the bike is designed such that if two spanners are needed to operate a fastener, the A/F sizes at each end are different (so, for example, they use a 14mm bolt head and 17mm nut).
Hence, making the lock nuts on the adjusters a different spanner size to the adjusting bolt could be a homage to the clever Japanese.