Well I don't think they'd outright refuse an eighth season if they deemed it necessary to wrap up things. I was just stating that the most recent statement from them regarding how long the show will continue for was 7 seasons and that season five would be when they begin down the slope to the end. Up until that point we all thought 8 seasons was the plan, because they always said they thought of the show as being a 80 hour story. Something made them say seven seasons instead of their usual "80 hours" statement.
And that "something" was very likely the fact that last year they signed a deal with Fox to write, direct, and produce their first post-GOT feature film "Dirty White Boys".
http://deadline.com/2014/04/game-of-thrones-david-benioff-d-b-weiss-plan-dirty-white-boys-as-first-feature-711666/
Then only a few months after this deal is made they say in an interview that they are doing seven seasons of GOT. I don't think that's a coincidence.