Makes sense but If I remember correctly my friend who owned and ran a mower sales/repair shop for 20+ years told me that in California those caps were installed to keep emissions down. The carbs were set lean at the factory and yes, they didn't want anyone messing with them.Everyone keeps saying that the tamper caps are on for government regulation..... that isn't the case.
They are on there because no one will leave screws alone who don't know what they are doing. They would take a new machine that wasn't running right and mess with those until it was way out of whack and them bring it in under warranty. Manufacturers got tired of people fooling with them and having to pay a warranty claim, so they capped them. It has nothing to do with regulations.
Now, the fact that everything is running super lean, that is for emissions. Less particulate emissions with a lean mixture. But they changed jet size to accomplish that. Even with a fuel screw, it's almost always still too small a jet. You bring it out so far and it can only get so much fuel. It's not large enough to be able to get too rich.