Well, the Stig made the Koenigsegg eat a whole tyre, so I bet the guys at Bugatti thought it would be a bad idea to let them drive the Veyron. It doesn't like eating tyres you see.
Well that's the point, they don't. There are millions riding on this: car-sales, sponsorship, the reputation of the whole company. At this level they are fighting for every tenth on track (okay maybe every second) so some doofus mechanic not knowing his job or not concentrating before or during a pitstop is not allowed. I don't think any of those mechanics are enjoying themselves during the race, they are working their asses off.
Indeed. You can make mistakes during a race and so can other drivers. If you recognize your mistake ( by apologising) and accept other peoples apologies there's nothing wrong. Just keep in mind that you're not the only guy on the track and a pass is only a pass when both cars survive.