I remember reading about it at the time. To be fair to The Guardian I construed that as being about the main stage, not the smaller ones. From what I've read, I think it was also a case of being the wrong band at the wrong place. They were fairly late replacements for U2 so I suspect many people would be disappointed about both U2 not being there and who replaced them. Obviously other acts have over-come that hurdle, but I suspect they have more recognisable hits to their name than Gorillaz!
As for people emptying from there, that's their prerogative but I personally wouldn't take a Glastonbury main-stage audience as a barometer for good taste!
But really, you're talking about one gig where people got upset because he didn't engage in much banter with them. It doesn't diminish the guy's talent AFAIC.
EDIT Just seen this on the comments on the Guardian page and I'll be honest I can't help feeling that this reflects my thoughts TBH. And if that sounds snobby, I can live with it!
"I'm not a massive fan of Albarn, but surely his ambition, and it was ambition, was merely to cast pearls before the lowest common denominator swine who go to 'Glasto'. I'm sure Take That would raise the metaphorical roof at Glastonbury... I think it's Glasto that deserves the criticism?"