You watch too much TV.
First, rape is not very common in prison. There are a bunch of sissies inside that are more than willing to take dick for a candy bar. You do see predators trying to run game on the younger inmates to see if they can turn them out, but unless you think you could be talked into that sort of thing, then it's unlikely to happen.
Second, most prisons are careful to classify prisoners and house them accordingly. So sex offenders generally end up housed with a high percentage of other sex offenders. This means you would very rarely end up with a situation where a bunch of other inmates are so offended by what another inmate has done that they deliver "prison justice". There are exceptions, but it's certainly not the norm.
Contrary to popular belief, most people in prison just want to get out, so they'll generally try to avoid too much trouble. And if they're never getting out they at least want to enjoy little things like TV and yard time that they could easily lose for years by attacking some stranger for no reason.
tl;dr - the story in the OP is news because it is the exception, not the rule.
