/disclaimer: I speak from personal opinion.
I think it's hard to find time or manpower to organise any such events when they're still busy with working with GPG on the new features for v1.2, Elemental and the usual busy things to do when running a business. They're not a large company like EA or Blizzard.
I think some of you are downplaying the arrangements required to get a tournament like this up and running, especially with the prizes involved. To get a 10% discount on all games, I think Stardock would either be required to contact every single publisher to agree to such terms, or absorb the 10% cut themselves. They would also need to make sure there is interest in such an event and that the publicity is certain. They're running a business after all and have to be wise with their resources.
That said, I agree with Ke5trel in suggesting the tournament only after v1.2, since that would hopefully make the game more stable and thus more suitable for such tournaments. Issues like the mystery lag and desyncs or what have you would have to go to make sure the matches are completed without incident.
