Current #1Cs:
Getzlaf, Vermette, Bergeron, Eichel, Monahan, JStaal, Duchene, Toews, Dubinsky, Seguin, Zetterberg, Nugent-Hopkins, Barkov, Kopitar, Koivu, Johansen, Galchenyuk, Zajac, Tavares, Stepan, Turris, Giroux, Crosby, Thornton, Backes, Stamkos, Bozak, Sedin, Backstrom, Little
Guys who could be #1Cs but aren't due to team-specific situations:
Krejci, Spezza, Datsyuk, McDavid, Carter, Plekanec, Malkin, Couture, Stastny, Steen, Johnson, Kuznetsov, Scheifele
Bolded the guys who had not signaled 1C potential by age 22, either by high draft position or by statistical breakout. Added strikethroughs to those who can be accused of not being 'real' #1s.
It can happen, but it's really quite unusual. Generally you're talking about guys who were either completely overlooked by the scouts (Datsyuk, Johnson), or who were drafted as bottom-6ers but turned out to have more skill than expected (Backes, Dubinsky). Rask will be attempting to join a third category, with guys like Steen and Plekanec, who flat-out beat the odds.