I think it's all about the combinations--versatility for power. Old-school concept. Consider:
Paragon multiclassing has a high cost: you lose out on paragon features, it takes 4 feats to get in, and the powers you get have a low level cap. But in exchange, instead of getting the 3 fixed powers for 1 PP, you get any of the powers you want from the multiclass, up to the level cap. Lower power, but a ton of options.
Same for the half-elf. One at-will power as an encounter power is liable to be your weakest ability. But you have, at present, 28 options to choose from, many of which (like Eyebite, Tide of Iron, Nimble Strike, or Commander's Strike) are situationally extremely useful.
The tiefling... it really sucks if you're not using a Cha build, because I see Infernal Wrath as being the race's big selling point. A tiefling wizard or tactical warlord blows. But a tiefling paladin, trickster rogue, warlock, cleric, or inspiring warlord can be pretty good, IMO. I'm really looking forward to dishing out a major smackdown with a tiefling paladin.