Gonzo knows exactly what he's talking about.
Wake turbulence floats down, you never want to be under someones wake. If you want to avoid it you need to outclimb them.
This is, as Gonzo has said, why you add a minute if the second aircraft departs futher down the runway than the first one. They come closer to the first aircrafts wake and extra time is added to compensate.
And there is to my knowledge nowhere that does take into account wind for departing wake spacing. Heathrow use time based separation but only for landing traffic. I have a faint memory though of someone who used to be in the RAF saying they would ignore wake spacing if crosswinds where high enough, no idea if this still applies though (if it ever did) and what the rules are for it.
In terms of the original question, in the UK 4 miles or time equivalent is provided between heavy heavy departures. However Heathrow and I think Gatwick are both excempt so there are few places this actually happens (Manchester, Edinburgh perhaps? Stansted?).