I've talked to some of these people and, yes, most of the stuff is built from scratch.
I'm doing research about the 'other possibilities' out there. I refuse to believe that you can only do something like that if you build it from scratch. I admit that the level of customization is limited if you descide to use something off the shelf, but one should certainly not have to invent the wheel completely new.
Seeing the limited reactions on this post, I guess there really is not that much out there. ;-)
Regards,
®ené