I'm going to try to discuss the OP.
I don't consider myself a Rat-Bastard DM. What I'm trying to do, however, is to create a feel of believability in the games I run.
I do believe that running encounters in the game that would be always in the APL-4 to APL+4 range of CRs creates a feeling of expectations and entitlement for the players, sooner or later.
I believe the characters are adventurers. As such, I think that a part of the believability of the game comes with keeping adventurers on their toes. Sometimes, they'll just mess with the wrong guys at the wrong time. Sometimes, they'll just be out of luck.
What I do, however, is always provide some sort of way in which the game might go on. If for instance they are level 4 and are searching for trouble in front of the Iron Mage, level 20 Wizard, he might just exile them in a prison half-plane for some time instead of just kill them. This is a new challenge. Or the guard, the Imperial Eyes, whatever intervene and arrest the PCs. How do they go out of jail? Or I provide some time to think about what they're doing: they are visiting Ghul's Labyrinth, enter a huge underground complex and spot a gigantic Red Dragon from hundreds of feet away - if they charge the Dragon, they're dead, but they've made the choice and could see that the monster was WAY out of their league. That sort of thing.
I think it's really naive to just pit the PCs against an APL +15 encounter by surprise, with the monster having a clear agenda of killing them, period, and expect the players to be happy about the results. The players being happy about the game is the WHOLE point of playing it in the first place. I just listen to the players and try to keep the game entertaining.