I was behind a relay tower, in line with the mixer desk at Donington, and the sound for Maiden was appalling, even worse than at Twickenham; I could hear every accent on the hi-hat, Bruce was fairly clear and 'Arry's bass runs were clear as a bell, but everything elses apart from the solos were totally muffled. I made my way forward so I could see better but the sound got worse, so I had to go back to my original position. The crowd around me were catatonic, mainly because they couldn't hear very well, and it was the worst experience of my 25 years watching Maiden. I'm sure the wind was an issue for those further back, (although it was not windy at all during Maiden), but I can't see how I could be ten yards away from a speaker and get such a bad mix?
It was also very, very quiet, especially compared to Alice in Chains and Mastodon earlier in the day, and Rammstein's set the following night was VERY loud and VERY clear despite being windier!
As far as the show being filmed, a friend pointed out a camera on a very high pole that was only there for Maiden's set, and there was a helicopter circling around for the entire of Maiden too, (which didn't help for people suffering from the bad sound), so I'm fairly sure they filmed it for release. Sky Arts did about 4 hours of footage for last year's Download so I'm sure they'll do similar again, I think Sky just took the feed from the video screens for that.