My 2 cents...
so to the question....
the run of the mill engine is designed for reliability and economy.
the HP engine is designed for MORE!
Take a stock 2bbl and add a 4bbl, its an HP engine
Add a more free flowing exhaust, its MORE
Change out the 2bbl cam with a 4bbl cam, its MORE MORE
Increase the compression either via compressor or compression ratio and its MORE MORE MORE
Put a cool decal on the intake and its MORE MORE MORE MORE!!!!!!
Back in the day HP and torque were good, but with modern machining, metallurgy and 50+ years of learning they have been able to best themselves several times over, get better gas mileage and be more reliable.