One thing that really bothers me is how the fluff insists that you basically must serve your patron in some way. Is it going to say the same thing for clerics? I sure hope so, because I despise with a passion the idea that a warlock is somehow more bound to their patron than a cleric to theirs.
And in any event, I don't think either fluff or crunch tying a character's class abilities to their relationship with an NPC has any right to an exclusive place in the game. Describing it as one way to interpret it, sure. Implying that taking that class means you have a master who you have to serve bugs the heck out of me--because it places classes on unequal footing unless it applies to all classes equally. If all fighters have a lord they must obey, all thieves have to maintain an affiliation with a guild to gain levels, and all mages must remain in the personal favor of the god of magic, then sure, warlocks can be part of the club. But singling out one (or a few) classes is absurd.
/rant