It is the law, but that doesnt make it right. It is a ridiculous law. Here in the good ole USA, there are thousands of laws, that dont make any reasonable amount of sense, but usually in some way, make dollars for the government.
The PDT rule has been in effect for many, many years - it was just never enforced until after the dot com rage in the 90's. I used to daytrade very actively with scottrade as my broker until they sent an email to all clients that they would begin enforcing the rule. I also found, by googling, scottrade and other brokers were fined large sums for not enforcing the PDT rule. If you want someone to blame, blame the IT gnomes in silicon valley who all quit their jobs to be daytraders in the 90s. After blowing thier accounts out they all went to the NASD and the SEC to complain. That's when the rule started getting enforced. They got their payback when they had to go back to work and found that their formerly $65K a year IT job now pays $10 an hour. And their PT Cruisers got repoed.