In fact a large number of supposedly straight actress are known as bi in the industry. They could all be bi and just be massively over represented or they could just be screwing whoever is going to get them on.

First, this sounds a lot like the all-too-familiar "Biphobia: Female Edition" in a nutshell. That is: "women who call themselves bi actually aren't (cuz there's No Such Thing of course)-- they're REALLY straight, just slutty!" (As distinct from "Biphobia: Male Edition", i.e., "men who call themselves bi actually aren't [cuz blah blah blah]-- they're REALLY gay, just cowardly!")

Second, since the vast majority of power-brokers in the entertainment industry are men... how would being bi (as opposed to just plain straight) help a woman "sleep her way to the top", exactly?

Third, the whole "sleeping her way to the top" thing itself seems pretty dubious. Both because it plays on the aformentioned bi-women-are-sluts stereotype, and also the centuries-old "actress = whore" stereotype (which, along with the euphemistic term "casting couch", is a convenient cover for what's actually just good old-fashioned sexual harassment). Regularly being faced with "fuck me or you'll never work in this town again, bitch" doesn't make YOU ambitious; it makes THEM predators. And whatever you do about it... you lose. When the one paying the price in this scenario should, by all rights, be the fucking rapist.

Fourth (and finally): I suspect that bi (and gay, and lesbian) people actually do account for a high percentage of the acting profession. Because we grow up learning to act, don't we? Specifically, learning to act straight. And thus developing a sensitivity to people's behavioral cues. So we know how to pretend to be something we're not... and hide who we really are.

In fact, I think that there's a strong connection between being LGB and being "creative" in general. Not because of anything inherent about us; because of the stigma that being same-sex-attracted carries, and the internal conflict that this tends to cause. Creativity/the arts are a major way of trying to resolve that inner conflict. Sure, anyone can have this kind of talent-- that itself is no more common for us than for straight people-- but we're disproportionately likely to focus on and develop it. Because (thanks to homophobia/biphobia)... we're disproportionately likely to NEED to.