I think the difference was having a tour manager - when Mika did a UK tour in 2010 everyone lined up behind barriers and waited their turn. At other (later) gigs people just mobbed Mika when he appeared, so he didn't stay. I remember one gig when he was trying to go down a line and the fans he'd already spoken to followed him and effectively stopped him from meeting any more.
London gigs are probably the worst as hundreds of people try to wait for him.