I'm with Basileus777.
That's exactly what you did by brushing it off as "just some fantasy series".
They're the ones who decided to adapt these books into a TV series - if they didn't have the moxy to go all the way then they shouldn't have undertaken the project.
1) It is "just some fantasy series", of course it is. But that doesn't mean it's not important to them, it maybe more means it's 7-years important to them, not an-entire-career important to them.
It's just a fantasy series for GRR. He puts it down and walks away and loses the fire and gets it back all the time. But he has the luxury of working in books where he isn't punished by actors aging out of roles or sets collapsing from lack of maintenance or viewers losing interesting if there isn't a new season every year if he decides to take a break from ASOIAF.
Total and Unwavering Passionate Commitment to working on one thing nonstop in perpetuity is a pretty unreasonable standard. GRR doesn't have it. Plus, GRR doesn't have to check his passion against a budget. Even if D&D wanted to include every single book character and do ten twenty episode seasons, they couldn't possibly.
2) I think it's a misreading to say they aren't "going all the way" with it. Presumably they believe that going seven seasons *is* going all the way with it. Seven seasons *is* the project they undertook. Seems like you have a different idea of what the project is than they do.
The series never could have possibly been a manga -> anime style "adaptation", spinning wheels on filler episodes for years while waiting for the "canon" to progress. Given GRR, the only way to do a page-perfect adaptation would have meant this project doesn't start until 2020 or whenever the hell the last book comes out. And even at that point, there would have to be cuts and interpretations to make the story make sense on the screen.