I mostly agree with the latter - I attend neutral games often, especially big ones. But GFs are quite simply priced out of range for this to be feasible. I don't blame people for selling off tickets.
I've been to 2 Roosters GFs and sat behind the posts both times, and 1 neutral because I'm close to a few Sharks fans and their first premiership was something I always wanted to see.
The price of a barely passable seat is minimum $200 these days. I won't sit behind the posts with an awful view now that I can afford not to. My money is going to travelling for the World cup.
And on a side note, the Grand Final day BBQ as a neutral is simply too good to pass up. 3 games of consecutive footy, 4 if you throw the Super League in, a backyard pissup with good beer and nice steaks.