Fallen out is a relative term, but at least two of the big buyers for HG DC war are no longer active. The keys still go very strong. But the random run issues of the ten centers can now be had for much closer to guide than the multiples they were bringing in 2008 - 2011. They still sell well, just not crazy like they were for a while.
That's kind of what I was thinking as well.
I haven't been actively buying war books for the last couple of years, but I can see that the good stuff is still good. By that I mean, keys, classic covers, and highest graded copies. To echo, Richard, finding nice shape (7.0 and up) 10 centers is still a challenge, but they've likely come down a tad in the price dept., or they will sit for a while.
To be honest, I'm now just starting to keep a close eye for these books again. If the price is right, I'll likely acquire a few more.