Leeway has been in the game since early 2005. It still exists to this today completely unaltered. The leeway we have in Classic and will have in BC is the exact same leeway that retail has now and has had ever since it was implemented.
Leeway is not some Classic thing. Unless you played the WoW beta back in the day, or during the first few weeks the game was out, you have never played a version of WoW without leeway in it.