The Killers were a secret set, Glasto loves throwing some of those in from time to time, it’s part of the fun. By the sounds, they are usually pretty last minute bookings.
It’s worth remembering Ed recently sold out about 5 nights at Wembley Stadium, I don’t like the dude, but his numbers are consistently staggering.
RE Radiohead, it’s pretty common for headliners to have much smaller crowds than mid-afternoon acts. The ‘legends’ slots regularly pull the biggest crowd of the weekend (dolly, Lionel, etc). From where I was stood the xx had a bigger crowd than Radiohead. It’s kind of the nature of the beast, it’s the time of day where there are the highest number of big acts playing simultaneously. Radiohead are, as much as I love them, a bit of a marmite act. Few people fall in the middle on them, particularly with their well known love for not exactly playing set lists that appeal to ‘casual’ fans.
A big act playing mid-afternoon are up against less big acts. Headliners are up against headliners. It’s crowd management, which is why you see less of the secret sets these days. Every fucker is on twitter, and it can get dangerous, which is why you sadly don’t see Radiohead & Pulp up on the Park anymore.