I know that is the common norm, but why exactly? Is it just to clean out the trapped crap, or to gain more thread engagement by cutting deeper threads?
I think I can make a case if the stud is already screwed into its last thread, cutting more threads in a taper tapped existing hole with a bottoming tap will only weaken the block.
Why exactly, is because you want the threads in the hole deeper then the threads on the stud. Period!
That is where we seem to disagree, deeper only weakens the block, whereas deep enough prevents your concern on jammed into the thread taper you are concerned with. There is a distinction The case you are arguing is what exactly? I tryd to explain to you the stress riser at the bottom is a wedge weekining the cast iron hole if the stud is not fully engaged. It's better to have room in the bottom of the hole for a few reasons, the stress riser being the main reason, but also because if the stud bottoms out they can be a PITA to remove, sometimes needing to be EDM'd out . It's a lot better for the studs threads to bottom on the very 1st thread then to wedge itself into the bottom of the hole.
Who here was disputing that? The stud is a far superior alloy so the stress at the very 1st thread is not a problem.
But whatever stress the the threads of the superior metal stud can handle, the block's threads must also be able to handle, the connection is only as strong as the weakest link.
I still want to know if you have ever installed a set of main studs?
For what purpose?I tryd to answer your question,
I agree will you answer mine ?
When you show it's a pertinent question, by all means
I do snug them a tiny bit 
