Upgrading is dangerous because of the chance of heart attack considering all the bugs and heartache you’re likely to encounter.
IMHO people shouldn’t be coerced into updating any more than Apple should be coerced into making their software run reliably when they release it. If they don’t care to make sure it’s ready for prime time (note: users are not beta testers, they are paying customers), then obviously the threat can’t be that serious, right?
What I’m getting at is that this essentially is a self-fullfilling prophecy and it works in Apple’s favor as long as people play their game by their rules. If a more considerable portion of iOS users were on older iOS versions, Apple could not afford to patch security issues only on the very latest. Sure they’d try, but then there would be some major hack, and publicity would be so bad they’d either lose market share or smarten up.