This argument about "forced fluff" is silly... what if I want neither Dungeons... nor Dragons in my D&D game? Would you (and rightly) say - "this game might not be for you?"
That argument doesn't compare well. If you were to say that you wanted dragons, but not the way they are described in the Monster Manual, that would be the same. As it is it does not pertain to this discussion because no one is saying that they want the ability to not include Sorcerers and Warlocks, they want the default flavor to be more open to interpretation.
And for the record, I wouldn't say the game isn't for you if you don't want dungeons or dragons in your game. I'd just say that you shouldn't put them in your game, because that works fine. I rarely include dragons in my games and dungeons are few and far between. Unless you count ruins and deserted cities and palaces made of clouds as dungeons, but that's a really broad use of the word that could apply to damn near anything at that point.
Reading the various posts about this topic, the 'No forced flavor' people just seem to be saying "Describe these classes in broad terms, that can be interpreted differently depending on who is reading it."
The Sorcerer uses and internal source of magic, give examples of what that source could be. That could be easily reflavored as a Wizard by just saying the guy is just a natural prodigy or has to study to control his natural ability.
The Warlock learns how to use magic through contact with supernatural beings. You don't even need to tie pacts to it, maybe you just want to play it as a Wizard whose mentor is an exiled Fey spirit. Her magic is slightly different from traditional Wizards because she's learning from a different school. Being forced to sacrifice your soul just because you don't want to go Vancian is fairly extreme. Lets treat it as what it is: a different way to explore arcane magic.
The classes can have baked in flavor, but leaving it open allows it to serve as inspiration without constraining creativity.
And seriously, never tell someone they can't play D&D without including dungeons and dragons. The game is much deeper than just its name.