The difference is a person is born gay, they don't need an operation to become gay. The Ed reflects this process. Hence you cannot be gayed, but you can become educated, indoctrinated, experienced, and transgendered.
Transgender does not mean having a sex change operation. Statistics say that somewhere between 66 and 90 percent of transgender people do not get sex change operations[1][2], and 40% have any no medical treatments at all (hormonal, surgical... anything) related to transitioning their gender[1].
[1] http://www.thetaskforce.org/static_html/downloads/reports/re...
[2] http://www.nytimes.com/2011/03/23/nyregion/23gender.html