"Historically, gay represented both homosexual men and women and technically still does," says Chris Crain, editor of the gay weeklies The Washington Blade and The New York Blade, "but a number of gay women felt that gay was too male-associated and pressed to have lesbians separately identified so they weren't lost in the gay-male image." That led to such names as the Gay and Lesbian Alliance Against Defamation. (The Washington Blade began in 1969 as The Gay Blade, a play on an old expression about a gallant.)Safire thus explains the usage. He doesn't opine about whether the wordy phrase should be the norm. I tend to think simpler is better, but it's helpful to have a good grasp of the origin of the longer phrase and the feelings it expresses.
Diane Anderson-Minshall, executive editor of Curve, a lesbian magazine in San Francisco, agrees that the one-word adjective was expanded to set homosexual women apart: "When, in the queer world, you say 'the gay community,' the majority of the time that conjures up San Francisco's largely male Castro District, or West Hollywood or 'Queer Eye for the Straight Guy,' so interjecting the word lesbian into the mix is a necessary reminder that we — gay women — are not simply a subset of that larger male world but rather our own distinct community of individuals."
A whole separate question -- which I'm just going to guess Safire has already written about -- is: when should people with a particular characteristic be called a "community"?