Well, excuse me if I'm wrong or if you don't really understand me (English is not my natural language), but I'm wondering why people around here have been tormenting themselves for... Well... Details. I do not find other word to describe that. First, I'm an Iguana, a Geth Iguana, so I can't tell everyone my sexuals orientations, and I hope you won't judge me as "homophobic" or as "a stupid adolescent jerk", but the fact that there is no male and male pairing in Mass Effect can be easely understandable :
First, Mass Effect is not what we can call a dating sim game, it's not like finding the true love is part of the main quest, you're out to save the world from the biggest threat in ages, you are going to fight the cruelest and wickest monsters in the galaxy... And you're wonderring why there are no homosexuals people in the Normandy ? Hell, this is not a game talking about how to make babies or not, it's a game with a great story and a great narration, with an incredible universe and complex civilisations and you're blaming the game for not containing one unique thing : No male and male pairing ? What the hell... It remind me of those guys who are blaming Mass Effect for not containing nudity or suggestive scenes, I can't understand those kind of people that only want naked body and big guns, Mass Effect 1 and especially Mass Effect 2 shows us very interresting way to approach some concept of love : Each "conclusions" to the "love quest" is innerantly poetic and interresting : Imagination is our only witness for those act of love, there is no need to show naked body shaking and panting, nowadays, people can't use their own imagination to describe love, they want films or images... And it's sad, because nothing is more equivocal and also obvious than this simple zoom on the bed on some "love conclusions" in Mass Effect 2.
But, I realize that I'm talking more about love representation in Mass Effect than our primary subject : Male and male pairing.
So, secondly : Bioware already suffered from wanting to let the player choose his sexual orientation. Remember when Mass Effect came out in the stores, there was the "Mass Effect Scandal" and the infamous Fox News interview (Even in the tropical jungle we know about this story) where a pretty uninformed (?) psychanalist was talking about Mass Effect as it was Mass Harem, treating the game to be lewd and debauched. I remember reading somewhere that Mass Effect was taken back from stores in some countries because it contained lesbian scene (Between the infamous "blue alien chick" and our Femshep). In our societies, lesbians are generally more accepted than gay people, it's sad, but it's true. The ancient Greeks were the only civilizations to laud masculine homosexuality over heterosexuality and feminine homosexuality, but they were often engaged in bizarre and wicked relationship between teachers and pupils... From the first muslims to the tribalest cult, women were free to love whoever they wanted, but men were punished if they loved someone of the same sex... Nowadays, it would be extremely risked and even provocative to release a game containing male and male pairing if female and female love isn't even tolerated or flayed.
Finally, I would like to say that you can't blame Bioware for "casting homosexuals" asides : In Dragon Age : Origins, homosexuality between male and male and female and female is enabled ! I also saw that you were reproaching the fact that in ME1, sexual orientation was only possible for FemSheps... Well... Personnaly... I play a MaleShep (I'm proud of him, his face is between Sam Worthington and Vin Diesel, I'm totally seeing myself in him XD) and dating our infamous Blue Alien Chick is not what could come to my mind in retrospect. Of course, for my first playthrought, I unlocked Paramour Achievement with our lady in blue, but now my heart is belonging to Tali... Ahh... Tali... Hrm... Well... So our Asari is litterally an Hermaphrodite : She can mate and reproduce herself with anyone of any species... It's... Kinda gross because she doesn't belong to any sex. If she wanted to sign up in Bioware Forums, she would take the case "Other" in "Genders"... Well... I prefer "real" females than strange beings between female and hermaphrodites...
To conclude, I want to warn you about the drift of that kind of behaviour : By wanting to see representations of homosexuals or transexuals, or zoophiles or whatever you're in (Iguanas only mate with other iguanas... Or Geth

... And Quarians

), you can be considered as a fanatic or a mad narrow-minded "blimp" (Is that the right word for "reactionnary old man ?). See the Avatar affair, with that gay group making strange attempt to show to hollywood that they didn't accepted that Jake Sully was not gay... What if in every media, they put homosexual main characters... What heterosexuals people would say ?
Well... I don't know if you will understand one word of what i've writtren (I hope so... Tell me if I must imrpove my spealing and grammary), but I think it's really trivial and fruitless to discuss about this or that game not including homosexual orientation for the main character... Because it's making the people angry, or tired, and it's a never ending story... Because when they include homosexual orientation in every medias... What will the zoophiles say ?...
Hm...