Just about everyone else has WS 3 (excluding Marines) so you'll be hitting on 3s anyway.
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...

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.