Now, I agree that eHarmony is probably being narrow-minded and foolish to ignore the gay community in its business model, but I don't think you're giving their defense enough credit. I've never used the site (or any other dating site), but I have heard the ads (which is what we're talking about), and it seems to me that their entire image is that they're a "different" dating site. The impression I get is exactly that they are a selective, "wholesome" dating site for people who are looking for marriage partners. Their ads drive two points home:
1) their matches work so well most of them end up happily married. (so I disagree that the product here is "love" -- for this site the product is clearly "marriage", at least in the ads I've heard).
2) they have a carefully crafted, studied, and validated methodology for making these matches.
From listening to their ads it seems that their target audience is people looking for long-term partners who have been dissatisfied with the results of other dating services or don't think "people like them" use dating services at all.
In this context, their refusal to accept gay clients, while perhaps economically foolish and of dubious legality, is not inconsistent with their public face.
First of all, if they have a carefully validated methodology, they would be foolish to jeopardize its success by applying it is cases where it may fail. After all, they also reject straight applicants that fall outside of their algorithm's parameters. (I can't agree with you that the dynamics of healthy, long-term gay relationships aren't any different than straight ones -- all of the gender issues, parental role modeling, and social pressures are different).
eHarmony claims it took them years to develop their algorithm before it was ready-- what would it look like if they managed to refine it for gays and lesbians in a matter of months? And how do you know that they're not gathering data to expand their algorithms to gays?
Secondly, if their clientele sees eHarmony's famous selectivity eased, or if their (more conservative?) customers see it becoming "just another" dating site for people who aren't planning on getting married, then it may lose its niche. After all, what happens to eHarmony's marriage success rate when gays and lesbians are allowed to join?
Don't get me wrong, I'm not discounting the possibility that eHarmony's refusal to accept gay customers outright is just bigotry. I'm just saying that given how hard they've worked to cultivate their image, their defense is a lot stronger than you give it credit for. Think about it: it's probably pretty good for their image that gays and lesbians are clamoring for access to their exclusive algorithm. Do these sorts of stories really hurt them?