Up-converted and playing on an 'HD' channel does not mean it is filmed in HD, and does not make it HD anymore then an up-converting DVD player makes a standard DVD become Bluray, or even HD. And yes, there are still SOME events on SOME sports networks (as I said, not ALL) that are not filmed in HD, and are not displayed as HD. I have seen this happen, even on D* systems recently, which means it is not bandwidth or allocation, but the actual network providing the programming. BB had display TVs and even ESPN HD (on D*) still uses up-conversion on programming for their HD channel. Its easy to discern it in the picture, even when the station AND the receiver do the up-conversion.
I will say that when sports are filmed in HD, in 720P, it looks good. Again, this was is not 100% of the time, and is likely event dependent.
EDIT- Even the 'Official Website' for ROOT does not say 100% HD, nor do any press releases, which is a huge marketing thing in this day and age (and a liability if specific performance is not adhered to). This would make the presumption that the channel(s) are not 100% HD all the time, rather then assuming they are. Even Starz does not claim 100% HD all the time on all of their channels.