It's statistically correct if your statistics take into account the fact that you might stop early. That's the point. It is more efficient to stop early, but you can't stop early while using statistics that assume you won't.
As I said, just because it happens all the time does not mean it's statistically correct. I've dug into enough statistical analysis to know that researchers whose field is not statistics simply do not understand statistics enough to know when they're screwing up. Most of them don't even know to apply a correction for applying multiple tests, and you're assuming they'll use statistics that assume they might stop early? Come on. You're imputing a lot more competence to the general case than I believe is actually present, which is my point.
