Unless Geneon were given a misleading HD master all those years back, one that was already upscaled.
There probably isn't much point to getting the first Blu-ray volume if you have all the eps on DVD already. I only ever bought the first one, and being a bit of a quality nut even when the upgrade is fairly minimal, I'm excited just to have the series in the highest possible quality. When you take an uncompressed SD digital master and upscale it properly, it'll look better than the DVDs. Such was the case with Samurai Champloo, but again the increase in detail and color reproduction is not greatly significant.
Excited for eps 6-8 though since they'll be native HD, and I guess the first The Dawn episode will be included.