I think it is fair to say that tieflings aren't standard fantasy. Pick up most fantasy novels and you pretty consistently run into variants on dwarves, elves, orcs, halfings, and gnomes. Those are the standard races in addition to human. In video games you see a lot more beastial races and stuff, but I say keep the standard traditional races (after all 4e is the only edition that introduces anything outside these core races in the phb) in the PHB and put the newer 4E races in a supplement.
Personally tieflings being in the PHB wont deter me from buying the books (because I will just ignore them along with dragonborne), but my guess is a lot of people are going to buy or not buy if certain races are included or excluded.
You aren't reading enough Fantasy novels. Or at least, not the ones I read.

And the idea of a bloodline cursed/blessed by outside powers is hardly a new concept. Nor the idea of a tough but dumb bruiser race. Also, as others pointed out, 'new' media enthusiasts make up a significant proportion of the target audience for DnD- it would be silly not to give them options as well in the core books.
My own personal dream? Since I love to run human- only campaigns, I would like to see some way to distinguish human characters from different backgrounds or regions like they did with Conan or Rokugan d20. but somehow I don't think it will make it in to Core.