So here's the trick...
The "rules" of never wearing brown with black or black with navy are because some darker hues of brown and navy can look ridiculously close to black. Ever looked at an item of clothing and debated with someone about whether is was black or navy? Well...when you wear a dark brown that looks like black, or a dark navy that looks like black, then it looks like you got dressed in dim lighting and you couldn't tell your brown from your black from your navy.
The trick then, is to wear browns or navys that are lighter in color and not to be confused with black. Then it looks like you paired the colors on purpose, and not accidently. Make sense?
I think these color combinations look great when done correctly!