If the content is live archival material, then that means it was shot in standard def. It's probably 4x3 as well, which means a squarish image instead of a rectangle. There's no reason to release a DVD quality picture on Blu-ray. It's a waste of money. When you release that material on the cheaper DVD, the picture is already the best it can possibly look.

Now, if we're talking about shooting and releasing a NEW concert, and you have the opportunity to shoot in HD, then that's a different conversation. But even then, you have to factor in the number of units you can potentially sell, in order to decide whether the extra cost is justified. Most disk duplicators have a minimum printing order of 1000 units. If you're only likely to sell 30 copies of a Blu-ray, versus releasing a DVD where you're much more likely to sell all 1000 copies eventually, then DVD is the more logical investment.