I used to work at the Wherehouse in 1995, we'd get all new stuff usually on Friday afternoon, with big signs "DO NOT SELL UNTIL XX-XX!!!"

I know sometimes retailers have broken street date on cd's due to them being pirated online, I know this happened with a couple of Enimem discs, but other than accidentally, has any retailer broken street date on a dvd/blu-ray release on purpose?

I believe it probably dates back to 1991, when Nielsen Soundscan started tracking sales of music & movies through software for Billboard's charts. Prior to that, I believe they relied on retailers reporting sales, which could, in theory, be inaccurate or manipulated. They measure the sales week from Tuesday to the following Monday. For studios and labels to maximize the number of units sold and gain the highest position possible on a chart, it made sense to follow the same schedule with their releases. That's also why they are always so concerned about street date violations. If something goes out early, it might debut on a chart early at a low rank, like No. 79, rather than the targeted No. 1. Sounds stupid, but how often have you heard ads that tout that a movie or an artist "debuted at No. 1?" Sounds more impressive than "debuted at No. 79, and then hit No. 1 the following week." It's all stupid marketing hype, and studios and labels can still do whatever they want, like "Harry Potter's" recent Friday release.