"Little Talks", by Of Monsters and Men, is a good example of this. So much time went by that I thought that mainstream pop radio was going to ignore this song. But that song eventually did start getting some airplay. It still has a bullet on the latest CHR/pop chart at the America's Music Charts website, moving up from 22 to 20. Meanwhile, over on the alternative formats, "Little Talks" is old news and even "Mountain Sound" has peaked and lost it's bullet.
This would seem to suggest that, despite the number of mellow folk sounding alternative songs being played on pop radio lately, that style of music hasn't really truly arrived yet and taken over. Songs with a dance beat still seem to be more dominant on CHR/pop at this time, especially on stations that were historically rhythmic leaning.
Even Hot AC radio is letting the alternative stations be the only stations playing the latest songs from groups like Of Monsters and Men, Imagine Dragons, Mumford and Sons, Lumineers, and so on.
But, yes, even songs that have more of an upbeat dance/pop sound aren't always played immediately. Maybe "Fireflies" wasn't enough to make Owl City "established" enough to get instant adds on all of the pop stations? Or maybe those of us who actively seek new music on the Internet are a minority and music is mostly just background music for a lot of people? "Good Time" is a good song though and I didn't mind hearing it on a radio that was playing at work today.