Rest assured that some Wal-Mart stores or Mom and Pop retailers will probably break the street date, the former due to lack of attention and the other because they figure they won't get caught. That's pretty much a given.
But the penalty can be severe, upwards of thousands per console sold. But yeah, you'll see people get their hands on them via unscrupulous means. I find it hard to believe Walmart would have them in stores now, though.
Typically they won't arrive in stores until about a week before launch to minimize risks of the street date being broken. At least that's how it was with GameStop when I was there. Big box may be different.