To bring in the "original characterizations", they'd have to re-dub the anime...Which would be a pretty big financial and time commitment to them. They probably wouldn't deem it worthwhile.
I do find it odd they haven't just released box seasons on DVD of the old season, though. Surely there's a market for it.
They have done. They're not blue ray, though. In fact, the only DVDs they're missing are of the Johto Journeys and Johto League Champions as they are now out of print in the U.S. They weren't box sets though. Thankfully, I own the Australian box sets of those. Most of my Pokemon DVDs are American though, as box sets or DVDs in general (excluding movies) haven't been released in the U.K.
Currently, the only box sets in the U.S. are:
Indigo League Orange League Masted Quest Advance Battle Battle Frontier
Also, all of Diamond and Pearl has been released on DVD and they seem to be currently releasing Best Wishes.
3DS FC: 1075 - 0819 - 0953 Pokemon White Version 2 FC - 2838 7984 6351