The T&L survey fails to meet even the minimum requirements for sampling techniques. What it measures is the relative scores assigned by those that a) read T&L and b) bothered to respond to the survey. Nothing else. You can't extrapolate from it, except possibly to the population of T&L readers as a whole (even then, you shouldn't swear on a bible). You also don't know what the experiences are of the people responding (i.e. they may have never flown DL), as the T&L survey doesn't gather that data. Heck, you don't even know if DL scored lower or was excluded for some other reason. It is pretty much worthless, especially as it differs so dramatically from the much more scientific JD Power and ACSI surveys.

I highly doubt that you have read any such survey in BusinessWeek. As far as I know, the only customer service survey BusinessWeek publishes is their customer service champs article every year. This isn't an attempt to rank airlines, it is an attempt to highlight high levels of customer service across industries. JetBlue is the only airline that made the most recent list, so there is pretty much no way to tell where DL ranked. Again, correct me if I'm wrong.