What you said bring up a question I've had for awhile. Are all the sports events required to broadcast in HD? If not then are we positive they start their broadcast in HD? I'm just asking. If Dish just transmits what is provided to them, then its out of their control. If it is transmitted to Dish in both SD and HD immediately then Dish needs to revamp their retransmission steps.
I'm sure there are no other complaints from other providers that broadcast their RSNs in HD 24/7. So I would say that the source of the broadcast is not the issue.
As MLB.tv has reminded me every commercial break during spring training for several years, "all regular season MLB games will be broadcast in HD." I"m not sure why they even put this up anymore. Several years ago some of the RSNs would broadcast some spring training games in SD. I watch a lot of spring training baseball every year and I haven't even seen a single spring training game in SD in years and I've never seen a regular season game in SD on MLB.tv.
So no, as Dare2be pointed, out it's not the RSN's fault. They broadcast every MLB game in HD. I'm not positive on NHL and NBA but I think it's almost certain that they broadcast all their games in HD too. Dish just doesn't carry the RSNs in HD and occasionally they either forget to flip the HD switch when a game is supposed to start or they haven't allocated enough bandwidth to HD sports.
The only way it will ever be fixed is if they turn on the HD RSNs full time or take some channels from HD PPVs on the days they know will be trouble. If they know that a Saturday afternoon in April is packed with more MLB, NBA, and NHL than they can handle they should reduce the amount of PPV movies available for a couple hours. It doesn't have to be a permanent shift for them.
Edit: and for some more confirmation. I watched the game the OP asked about in HD with MLB.tv this Sunday on the Fox Sports Detroit feed. It was most definitely in HD right from the start. The only place it wasn't was on Dish.