Ah, how parlance varies.
'Edition', for most RPGs, implies 'revision' more than anything else. D&D is one of the primary exceptions, where 'edition' implies 'total rewrite' or thereabouts, in more recent times, anyhow. So, actually, it's 'modern' D&D that is one of the *only* exceptions I can think of. It's likely that I, or someone else here, can come up with a few others, but even if so, they're
vastly outnumbered.
I favour the 'revision' approach, except when 'total rewrite' is in fact necessary, in order to improve the game (i.e., not just a means of making more money, without giving a damn about anything that really matters, like quality). And. . . I'll leave it there.
But anyway, yes, WFRP 2e is a case of revision, most certainly. And 4e? Nope.