I think when you're looking at the cultural aspect, you want to look less at orientation (homo vs. hetero) and more at the identity politics and the cultural norms that surround it.
Queerness is very much grounded in a type of counter-cultural action against the mainstream and it used/uses the body as a performative space (in the same way that most subcultures do - look up bricolage) to make a statement. It's a disruption of what is 'normal' and 'straight', hence the movement's appropriation of the slur 'queer' and this too reflects the coming out process where we make a statement about who we are that a straight person does not (look up heternormativity). There are also many subcultures and groups within the queer community, many which don't line up: bears, twinks, dykes, drag queens and kings and so on.
Straightness on the other hand is not explicitly about being 100% heterosexual as there are people who experience attractions to the same sex as well on their own who don't identify as bisexual. There are also heterosexual transpersons who still identify as queer. There are also bisexuals who identify as gay (which is not interchangeable with queer) simply because of the identity politics. This kind of thing is brought him with men who represent themselves as 'str8 actin gay male'; there are notions of straightness and queerness which extend beyond who you want to be with.
As for 'gaydar', as it is/implies a form of detection that means that any genuine gaydar would be based on working past the stereotypes to uncover what is not explicitly there. As a gay male I can say that yes, I do have some facility with detecting others but it's more of a conditioned thing; needing to detect certain cues and tics so as to breach the normative barrier but these cues do not work on the stereotypes within the queer community.
Interestingly though, I find it easiest with gay and bi (cis)men, there's often just a feeling that I get with those but this is much harder with women and transmen where I can feel the more rational mind taking over. I know I am far more accurate in detecting say, a trans person, than most of my very straight friends but I suspect that this is partly through exposure and because I let myself think about it lucidly. A truly open mind can go a long way and may serve to explain a lot about 'gaydar'.
I also do think most completely straight/hetero/cis persons don't really have a gaydar, no matter the claim. In that instance I personally feel it could only be based on stereotypes or social surveillance which admittedly can be accurate sometimes but it's certainly not the kind of thing you could label as 'gaydar'
Kwayera's suggestion is also good, there's a lot to mine on the biological area.
I'd also advise you, if you ever get the time, to dig into queer history: Stonewall riots, Harvey Milk, the links between the rise of feminism, queer theory and the free love movement, the evolution of the rights and definition argument from pathology to sin to lifestyle to biology to natural rights and determination. There's also the comparative development, and lack thereof, of queerness between the West and Eastern Asia and how that's changed thanks to globalisation. This isn't explicitly gaydar related but it's general grounding in the topic which can help you understand what it is that you're asking about.
Well, it's a clever topic, first off!
I think heterosexual v. homosexual could work for cross cultural...maybe survey people from both groups and see if homosexuals have a stronger sense of GBLT people in a near vacinity...
Um. Homosexual and heterosexual aren't cultures, sub or otherwise, they're orientations. So no. That kind of oversimplification is moronic.
