Yeah... just about everyone except for Marines, Necrons, Kroot, Chaos Space Marines, Daemons, Dark Eldar, Ogryns, Aspect Warriors, Storm Guardians, Grey Knights, Orks, Hormagaunts and probably a few dozen other units...Just about everyone else has WS 3 (excluding Marines) so you'll be hitting on 3s anyway.
Not quite sure what you're getting at here really. WS 4 is very far from uncommon. In fact I'd wager that more units have WS4 or higher than don't.
Sure, it's kind of a pointless rule if you're up against Tau or Imperial Guard the whole time, but against the majority of enemies it will be a rather nice edge in combat.