[DOM Level 3 Events] optionality of the capture argument in addEventListener/removeEventListener

There are modern browsers that made 3rd argument in the
addEventListener/removeEventListener be optional. Is this a legal step?
If I understand correctly, specification requires 3rd argument to be passed,
thus the new behaviour not backed by the change
in specification only destabilizes web as a platform.

Personally, I like the behaviour, but cannot use it as long as not every
browser does that.

Sergey/