I can only speculate but I think they ran into some seriously bad problems. Are you sure the address is ghasts.com and not pr-mc.com?

See, when I check server index it tells me they're offline (duh) but also how this should be a network of servers. If I then compare this to the server entry on PMC you see the same thing: offline but also "network of servers" in the description.

Now: notice how both entries provide a different server address? That's a bit strange.

So now the reason why I think they ran into issues: the entry on minecraftservers.org. I mean, seriously: "Hacked by Team_Klinux"? That looks plain out bizarre, yet this is exactly what Google pointed me to when searching for Pure Realms (also note that the owner name does match).

It's pure speculation but my guess is that they got overrun.