Yes, that´s the explanation, they were included until the last revision of Sonar Platinum.
I think you should be able to install just Blue Tubes by choosing custom installation in X3, I´m not 100% sure, but I think the Blue Tubes plugins in X3 are the latest version. Nomad´s own installer has only had other plugins added to it, if I remember correctly.
This forum sticky has a chart describing the differencies between the versions:
http://forum.cakewalk.com...-4282018-m3750958.aspx