Re: Those huge arena events...
A university weekend LAN in Essex, with an attendance in only double figures, was more than enough to keep the 'dry roasted peanut' odour in the atmosphere. Not only do people smell after sitting at their pc for up to (let's be generous here) 8 hours, but working machines also smell.
PCs are not hermetically sealed boxes - dust gets sucked in, dislodged, blown around, PC components get hot, things start to smell - dead skin, hair, food, general heated stuff.
On top of that, consider the environments that these machines could have come from. No one runs their gaming PC in an airtight chamber, and not everyone has good habits. Even if only 5% of attendees are smokers, their PCs will still stink the place out as they heat up. Smokers make for foul PCs.
Maybe you ought to rein your neck in and get your own prejudices in check before having a hissy fit, huh?