I believe MLBtv is now included with extra innings
https://secure.mlb.com/tv/activate/?&affiliateId=mlbMENU
The one year I got NBA League Pass, I asked about that, and the reason the CSR gave me was a marketing reason. It is listed in SD as all the games are guaranteed to be SD. But if they listed it as SD/HD (which I think it was for a little while), someone could buy that assuming that they would be able to see all the games in SD or HD. But there are still some games that aren't in HD.NBA and NHL packages only list sd as well. It may be you pay for HD (with other packages) or have the HD for Life.
My guess with Extra Innings is that it will be the same as League Pass - almost all the games will be in HD (except for if both teams RSN's aren't carried on Dish or Dish is out of bandwidth), but it is being presented as SD so that someone couldn't come back to Dish and say "it was marketed as HD, why is my game not in HD."
Bandwidth always seems tight with Dish. Don't they have any new satellite plans? Since Direct announced their 4k plans, I would assume Dish has to follow suit.I'm guessing they will have more bandwidth, with the 8psk transition. Granted, that's not until 31May.