It's nice to have one but it's not the be-all of openside play. You can force turnovers with good counter-rucking and it has pretty much the same affect as you would if you had a pilferer.I disagree uce. A good #7 or a ball-pilferer equivalent (e.g Henrich Brussouw #6) is very important for a team's success.
David Pockock, Richie Mccaw, Heinrich Brussouw are the sort of players that will literally force turnovers or penalties; these players can shift the momentum of a game with that one ability; even if its only a couple of times in a game.
No one wants a reminder, but remember 2007 RWC where Tonga were on fire? Their above-par performances were due to one Nili Latu who had the ability to steal opposition ball at the ruck.
Samoa needs someone, i just hope they find one before the RWC, or devise some plan to replace this defficiency!.
I'd also like to note that ever since the rule changes, McCaw's turnover numbers have gone way down and I wouldn't even class him as pilferer anymore, but that doesn't change his effectiveness in matches.