I think this perception of what DL is, is a bit off. Contrary to what the company likes to think about itself, DL isn't a luxury or exclusive product. At the end of the day, it's transportation. And they need to fill their planes by catering to a wide variety of customer. That's why they don't just sell D1/F and C+... they also sell BE at the back of the bus, and they sell tickets on online TAs like Expedia, whose clientele often shops by primarily by price.

You know what's really important to the biz travelers? Schedule/frequency. No way DL can fill planes in high frequency markets by just catering to the "premium" crowd.