Dave,
I remember that old rule. It used to read something like; the absent player could respond if he were within "earshot." I agree, the newer ruling is much better; kill the hand immediately after dealing the last down card to the button. If I can go back a few decades, I can recall when smoking at the table was a regular occurrance, even cigars. Back then, as a comon courtesy to the dealers, the only seats at the table that were non-smoking were the one seat, and the ten seat, (or even the eleven seat, that's right, some hold'em games seated 11). I mention this because when smoking at the table was no longer allowed, players used to run back to the table from the break area yelling "here I come," or "I'm here," or they would be really mad if you dealt them out, or killed their hand while they were sprinting back to their seat, still spewing their last gasp of smoke over the table. For some of todays dealers that complain about their job, how would you like to clean out ash trays on your breaks. Ah, the good old days.
Dave, you are absolutely correct when you said; " In short, the rule to be "at your seat" seems to have been a good solution to a myriad of problems.