If anything, Wilco would have been the one they replaced Arcade Fire with.
Nooooo way, dude. Just no way to that. Both Death Cab and Modest Mouse played Sasquatch as subheadliners in the 2-3 years leading up to 2011. I'm sure wonk will punch this statement full of holes, but I'm pretty sure that Wilco is a headliner roughly on the same level as the MIGHTY FUCKING THE MIGHTY FUCKING WEEN.
And yeah, up to and including (arguably) Good News Modest Mouse had one of most impeccable discographies this side of R.E.M.
Well of course Death Cab subheadlined the previous time they played, they were before the mutha fuckin Cure.
Regardless, Death Cab is a big name in the "indie kid" scene, which Sasquatch mainly caters to. They played the Key Arena and Memorial Coliseum after they played Sasquatch, while Wilco played the Paramount and Schnitz.
Also, last.fm listeners is usually a good way of determining how popular a band is.
Death Cab for Cutie: 2,411,728 Modest Mouse: 1,963,387 Wilco: 1,033,007