[nkurz]

You're right. I was being sloppy.

I should have said something more like "the standard deviation calculated from a sample set is only generally applicable in so far as one is willing to make assumptions that the sample set is representative of the distribution as a whole". The default assumption in traditional statistics (such as quoting p-values) is that the distribution is normal, and in real world situations often not the case.

Your restatement is right on, although I'd go farther and say that standard deviations (and confidence intervals) are only useful metrics with regard to the particular assumptions one is willing to make about underlying distribution. Yes, you can calculate these measures, but they won't help you if your assumptions are irreparably flawed.