My hypothesis is that you choose based on optimization or flavor (and more likely a mix of both) and that is a matter of the player and not really of the rules. If you were optimizing yesterday, you'll be optimizing today, the results will just be different. NOW, IF the races are much closer to all being equal for a given class then maybe you will pick based on flavor between those options. I'd have to be convinced though that at least a big chunk of classes end up with that greater equality.
I fall into the "mix of both" category (which I too agree is the most likely scenario - people want to play what they want and not suck while doing it). So for me, adding an extra stat boost option is a very cool thing because some of my "suboptimal" builds can now be just fine.
Sidestepping the dwarf melee combatant debacle, let's look at a hypothetical scenario (heck maybe this is accurate and I missed it). Let's say the tiefling is updated to be +2 INT and +2 CHA or CON.
Prior to this, I'm sure there were plenty of people that wanted to play an tiefling infernal pact warlock (and they probably did). But now if they do they are less suboptimal because they can elect to get a +2 CON. Or perhaps a CON build wizard for a tiefling. Or a tiefling battlemind. And so on.
My point is this: The stat boost changes are not providing you with options you didn't have before. Rather, they are making several options less suboptimal.
Now you're thinking "you're getting a little close to contradicting yourself Tyrlaan." I don't feel I am and here's why:
(a) People don't want to feel like the weakest link in a game AND (b) Optimizers will be happier with their "suboptimal" counterparts in a game, and vice versa.
What am I getting at? If Joe Schmoe is playing a tiefling battlemind with a 16 CON because that's what he wants to play and Bob Diddle is playing a goliath barbarian because it's a 'gold'* build, there's a good chance the two will be at odds as the game progresses. These are dueling player mentalities. But if Joe Schmoe can play said tiefling battlemind and pick +2 CON during chargen, well, he probably has an 18 now. The playing field has been leveled, at least to some degree.
Stat boost alternatives provides additional options to build characters that "don't suck."
For me, that's reason enough to be just fine with their introduction to the game. Conversely, what do they bring to the game that's a detriment? It's not really clear to me why they can be a bad thing.
*As an aside, (a) I used "gold" because I think it's the best of the best as per the color scheme labeling on the char ops forums, (b) I have no actual certainty that a goliath barbarian is a 'gold' choice, and (c) I actually find the whole color coding for optimization kind of irritating in a way that I've yet to find the right words to put together to express it and I'm saddened to see them creeping into enworld posts (and I just did it myself

).