I'm not sure where you're getting that information -- that's not even true for master feeds from C-band.Even most college sports is in HD.
It's all dependent on which production trucks are used for the broadcast. While all the RSNs have HD broadcast feeds, getting the game video packaged is still reliant on the production trucks at the venue.We are talking about the sports pack, which means RSN, so games in HD or SD on OTA broadcast are of no concern. All Pro sports on RSNs are now in HD. If the provider carries the HD broadcast is a different issue.
For a quick behind-the-scenes for the production trucks, you can check out this video: Inside the Rays: TV Time
And there are still a number of trucks out there that are still primarily SD broadcast vehicles. See this article about the truck used for Angels spring training games: Coastal Media Hybrid Truck Helps Fox Sports Boost Spring-Training Coverage, Cut Costs : Sports Video Group