You're got it partially backwards, a funded game can create more motivation to improve the game. For example , the guys that work on Dota have real jobs and things they like to do, working on Dota is a hobby.
On the other hand, this IS Stardock's job. There are plenty of reasons for support after sales, keeping a game going is easier than going through the entire game making process. Continued improvements will lead to more sales, an example being DoTA. If you recall DotA wasn't very popular until after quite some time after it was released and slowly improved, thus increasing the amount of people that downloaded it and played it.
This will lead to an expansion usually which generates more sales of the original game and profit from the expansion in a way that's much easier than making a full game.Also, Stardock and GPG are thinking about opening up mods, which alone will create oodles of content provided the game has a big enough fanbase. I think they'll be just fine.
Best example? Mother freaking Starcraft. Blizzard makes so much god damn money off that game and they haven't touched it in way too many years. It's like money that keeps falling in their pockets. Good game, by the way. You should play it, if you haven't..