Then why is it your problem? The user could put in a sleep 1_000_000_000 as well, or use a billion other ways to slow down the entire program.
It's his problem, because he's more concerned with actually accomplishing a task, rather than conforming to some bureaucratic "rules" about what is and what isn't in his job description. And since he's building verilog tool, I'll bet his "users" are highly educated engineers who are trying to get actual products out the door and he's trying to prevent any unnecessary slow downs caused by inadequate knowledge of perl trivia on the part of his users. I'd guess he is not attempting to prevent his users from being malicious. In my mind, I picture this scenario: they've got an IC tapeout 1 week away, and one of the 20 engineers on the project has tweeked some his tests a little at the last minute (to better catch bugs, because these bugs cost $1+ million in NRE per spin for a 0.1um CMOS process), and it now uses $&. It runs fine on his tiny test circuit, but when it gets rolled into the full 100 million gate IC, the test that used to take 5 hours now takes 100 hours. Oh, and they probably lose $50,000 a day in revenue for every day they slip (ouch).
