Jade Empire is another Bioware game with same-sex romances (and imho the best done ones too).
While you may not think Liara counts she looks female to the human eye and thats enough for the vast majority of people to include this as a same-sex romance option in their minds. I'm sure the vast majority of people who romanced her as a female Shepherd were not going "wow romancing this sexless alien is great" (although thats a debate for another time).
Back on topic as a gay female I'd quite like to see same-sex romances in the game at some point, but there are way more priorities to be sorted before this is done.
Making Liara genderless always felt like a cop out clause to me; get the best bit of having ***** pre-teens shagging something that looks female, but actually isn't, therefore they can justify male Shepard not getting into Kaiden's biotics.