"I asked a Kubota salesman about the usefulness of 16hp in the B7400, he told me that diesel horsepower was different than gas horsepower."
Actually, he was right in a way...
There's gross HP, net HP, JIS HP (Japanese standard), Din HP (German standard used throughout Europe) all of which will give you different results for the same engine.
And, of course, we also now use Kw to measure engine output.