I wonder how much authority the crappy site has...? and i wonder if that can make it harder for google to punish a site that it may already trust? Then again, we may not even know the full story... only one side is is saying that it is a cheating crappy site... maybe the accuser is the cheater, and the other site is legit.. thats like the other party showing up to court for a ruling, and I never even got the notice to show up to defend myself...
Really loved your last example. I've personally had numerous clients who enjoyed great exposure from Google, yet found themselves being penalised a while later, without changing their marketing or content strategy. Unfortunately, I've met a few who had their Adsense accounts disabled, after gaining a decent income from them.
You can’t conclude it’s because of crappy backlinks. Sometime the site you are referring may have other important SEO factors. Backlinks are still important for SEO. But it is less important compared to pre penguin era. If you are doing your SEO correctly you don’t need to worry about crappy sites. They will come and go. But you will stay for a long time.
Actually google now ignore the bad links as they said. So, basically if you spam your website google will consider only the good links.
Up until now, Google algorithm is not fully efficient. I have also gone through similar experience but, Google is continuously updating its guidelines and in future, these sites may be impacted badly with penalty.