Part of why Game of Thrones is so popular is the really good writing of Martin so with Herbert we got that covered too.
The other part is the pitch perfect casting.. people like Dinklage playing Tyrion, Charles Dance as Tywin Lannister or Lena Headey as Cersei. If they could find actors with the same skill and presence then i believe Dune could also be a hit.
However Dune is an older story that isn't well known outside of SF fandom as opposed to Game of Thrones which i have seen being read by many non-Fantasy or genre fans so i don't believe there is a lobby out there that could push HBO to invest the same kind of money into an old story.
And mind you.. the first season of GoT also was not that heavily financed. Only after the show took off like a rocket did it get more money.
But i'd love to get a comparable Dune series, at best with the visuals of the movie (love the style and totally fit the universe) with some A list TV/Movie talent to play the characters.
Who would be your choice to play the various key characters such as Paul, Jessica, Baron Harkonnen, Gurney or Stilgar?