Maybe another way of putting this is that one who defines themselves as a crossdresser will see what they do as gender expression whereas one who defines themselves as a transsexual will consider what they do as gender identity. Both of course fall under the transgender umbrella.
I feel that due to the fact that trans people are relatively scarce, it is more useful for an organization to be transgender-friendly as a whole rather than be specific on just one aspect of trans behavior or identity. Say you have a group specifically dedicated to transsexuals and another dedicated only to crossdressers, it leaves out all of the people who are still questioning their identity. Often TSs considered themselves crossdressers at first and generally "cross-dressed" before going full time in their new gender role. It is therefore quite likely that a lot of the CDs in a group like Tri-Ess may actually be TSs but have not yet come to terms with that yet. Such an organization with its restrictive focus can be counter-productive to anyone not 100% sure of their identity. The same goes with a group specifically on TS issues. A person who is not yet 100% sure they are TS will avoid such a group because they won't be able to "keep up" so to speak.
Obviously, people can form whatever groups they want but I personally think that any group that excludes certain segments of transgender identity and expression is going to be counter-productive in the long run to a lot of members or prospective members. Even in major cities, it is not like their are trans people everywhere so being the minority that we are makes it more logical not to unnecessarily divide ourselves up further.
