It seems to me that
Drake Mallard's node
conflates two distinct issues: first, the assumption that any
random person walking down the street is probably
straight; and second, that
homosexuality is still generally thought of as, if not
wicked like it once was, still at least a little
naughty. These are two separate issues and should be treated as such.
He (I'm assuming D.M. is a he, with a name like that) has a very good point that TV and other entertainment still for the most part sets homosexuality aside as something of a novelty or "adult situation" (though there are a few notable shows like Buffy the Vampire Slayer that eschew this) and I completely agree that this should change.
There is, however, the issue of the perceived bias that is show by, per M.D.'s example, gearing Valentine advertisements toward heterosexuals. This and other similar perceived biases are based on the assumption that most people are straight. Well, most people are straight. This sort of thing is very much like the issue of left-handedness. Take scissors, for example: about 90% of the scissor market will buy one kind of scissors- those made for right-handed people. It doesn't make sense for them to feature a lot of left-handed scissors in their advertisements because not as many people will buy them. This doesn't mean that scissor makers are right-handist, it just means they're advertising for the larger audience (after all, only fencers and reactionary second grade teachers care what hand someone favors).
In fact, I hope that eventually homosexuality will be treated like left-handedness: mildly uncommon but nothing to get uptight about.