"The pens are all the same, and dozens of people make comconsoles - if I have competitors later then this will presumably be less true, but for the time being the pens can securely talk to each other as much as their operators want without the setup rigmarole of consoles. If Cordelia has her pen on her person - or if it's upstairs, even - then I can send her a 3D drawing or whatever else I like without having to do anything more complicated than identify who I want it to go to. Getting the pen to talk to the household network so I could do things like talk to my manufacturer about Vorsoisson's pen was more complicated."