It is, but so are deadlines. That's why first batches are always a concern. Again, it's not like all units will burst into flames and have all their buttons fall off, but the risk of getting a faulty unit is always greater on the first batches as on later ones.
Example. First batch of Note 3's had a wobbly home button; newer units don't. First batch iPhone 5S's have issues all around, but most notably, with the battery. Newer batches don't. On the software side nearly all new devices have to release patches to fix something that doesn't surface until the masses begin to complain; first batches will run the risk of having something not work properly until said patch is released.
I'm not saying buying first-batch articles is a mistake, but he asked if it was a legitimate concern and, truth be told, it is. The risk, however, is not THAT bad, especially when all you want is your new toy with you.