As far as I'm aware Arcade Fire sell a lot of albums worldwide, so commercially they were a safe bet. Mumford and Sons closed the show last year, Arcade Fire opened it this year. Think Mr Eavis might be in need to hand over the reigns.
May well have spent over the odds getting the Stones last year and had to reign it in since
I think financial reasons are almost certainly behind this - either that or Eavis is no longer able to distinguish between a musical movement and a silly fad.
It's just a shame to see Glastonbury going so far downhill. It used to have huge acts headlining, the very smallest of which would be the likes of Kasabian - now bands like Arcade Fire are making Kasabian look like a big act.
Metallica are obviously huge in their genre, but even they probably aren't the kind of act you'd expect to headline Glastonbury (maybe on the other stage).
I just don't see how it can be tough to get the really big acts in. They charge a lot of ****ers a lot of money every year - there must be plenty to throw at quality bands.
**EDIT**
If the Fleetwood Mac rumours (pun not intended) for next year are true then that's back to what I'd expect.