This is definitely true. I contacted Mises.org about publishing my Bitcoin article. Of course, they rejected it because they said it would "appear to be a promotion". I think they're worried about the legal ramifications of it.
I guess Mises is too academic anyway. Best to spread the word to other groups that would be more willing to endorse it.
Nice that you tried. Once I have some time I'll do the same. Maybe multiple people writing them might convince them to at least read something about it.
I tried with Brazilian Mises Institute as well, and they also rejected so far, apparently because it's money "backed by nothing", as said above. I'm waiting a little before trying to explain them the difference between bitcoins and fiat currencies, but I'll try.
Maybe this deserves another thread. I'll start one and see what happens.