Jek, there's an argument about this, because, put simply, "open source" means something very specific.
As a friend once said, "Redefine 'work', and anything works."
Its a bit the same, if Cyan wants to redefine "open source" they can go ahead, but don't count on anyone else taking them seriously after that.
Open Source is a fairly well defined term, and here is a link to the actual definition.
http://www.opensource.org/docs/osd
Cyan has said that they plan to release an "open source" Uru. I don't know about you, but, personally, I'd personally hope that Cyan Worlds has not been leading us on with false promises. I'd personally still be happy with Plasma being open sourced, and the content under a less permissive license, hopefully one that would still allow us to make changes and distribute them, but, if at the very least Plasma is not under an open source license, then, I'm going to be pretty ticked off.
If you want me to give a reason for being "pretty ticked off", well, I've been watching and patiently waiting, sometimes not so patiently, at times. I've been holding out for the release of something that would benefit the community in general, I've been waiting, when to be honest, had I not've been told Uru would be "open sourced" I would've faded into the background, gone and put my efforts into something else entirely. "Open Source Uru" has kept me interested, has kept me willing to support Cyan. I'll be buying a copy of MQO, since MOUL's closure, I've bought two copies of MystDS, a copy of realMYST, a copy of Riven, among other things. I'd hate to find that I, along with many others, have been strung along, with false promises of an "open source" Uru.
Hell hath no fury like a fanbase scorned.