You do realize that plenty of games have lines that are gender specific said by the other gender. DA2 also had male hawke say lines that were femhawke only:
Cullen was never going to be bisexual. He never showed interest in guys before and those lines were only included for the same reason the video had similar lines done by the other VA. Man, DA2 really turned the LGBT fans into spoiled kids who want the entire game to be to their standards.
Actually, considering that David Gaider, Patrick and Karen Weeks all mentioned at GaymerX there was a character that they were trying to write as bisexual and couldn't quite pull it off, it's a good chance that Cullen was meant to be bi at some point in development. Once again, someone can be bisexual without telling it to everyone they meet. Plus, this was the first time Cullen had actually gotten to know a PC enough to get to know him in that sense. I don't go around telling people that I'm bisexual everywhere I go.
Cullen was also in his early 20s during Origins, which can be a big point of understanding one's own sexual identity as an adult. In the end, he was meant to be straight, but no one should throw any around any certainties as to whether or not he was "never" going to be bisexual.
As to the bolded, you obviously have no idea the number of threads/posts coming from guys declaring they were straight men and wanting to go back to DA2's method because they weren't happy with Cass and Josie. So no, it isn't just the LGBT BioWare fans. If anything, I've seen several members of the LGBT fanbase that are opposed to the all bisexual system. That includes me and I guess I have to say once again that not all LGBT fans think alike here.
I personally feel that it was cut for a reason, whether time or characterization or both (sorry, I'm not taking an anonymous "ex dev" tweet as gospel truth), then I respect the developers decision. I don't want this forced back into the game at this point. However, I don't feel the need to be rude to everyone that feels otherwise.