HBO have a nasty habit of axing their expensive epics after two or three seasons (Carnivale (2), Rome (2), Deadwood (3), when all needed at least one more run). It'll be interesting to see if they stick with GoT.
To my understanding Game of thrones was a massive hit so far.
G.R.R. Martin is a beast of an author, GoT being perhaps the biggest epic series of books written so far^^
and I guess they'll continue to produce it, since Martin himself is co producing and people just love it.
Haven't watched the other shows you mentioned, but I'm positive GoT will be finished.