Before this turns into a firestorm, I will just say that I don't think you meant to make that sweeping generality based on however many articles you've read about Prop 8. You're use of "they" refers to the small number of black Americans that those articles could possibly address. I will also assume, perhaps to my folly, that you know articles about minority groups are rarely written by those of the group.
That being said, here's my take on the parallel between gay rights and the Civil Rights Movement. A social culture based on shared traits and preferences is not the same as a culture based on ethnicity. You are raised with centuries of tradition in an ethnic culture. A social culture is what the predominate class makes of it, a zeitgeist. Very few gays are 'raised gay'... what does that even mean? No matter how I dress, talk, style my hair people will know I am of African descent. I will always face some kind of prejudice because of this. No has to know about my sexuality. Even if it was apparent, I would still face less discrimination based on my sexuality than on my race. (There's a RJ topic on that.) People focus on the things that affect them most. Simply said, being black is harder than being gay. Therefore, the plight of gay discrimination is less than the plight of racial discrimination. Additionally, hetero-America doesn't understand that sexuality isn't a choice. Black America is no different. Gay culture is also seen as a white culture. Generalizing hetero-Black-America... whites, who as a whole have more privileges, making a choice to open themselves up to discrimination, lack the perspective to compare their struggle with the Civil Rights Movement.
What you say about gay America being discriminated against, tortured, killed... all very true. However, what is presented in the media is educated, whites with money complaining that they can't take their boyfriends or partners to the company Christmas party. Those pale in comparison to the daily struggle of many blacks. Take a look in a history book and you will find many more stories of mutilation, torture, gruesome and senseless murders of blacks... done publicly, with no threat of prosecution, no closure for the families of the victims. The upstart of the US economy was built on the backs of slave labor, and to this day blacks are still steadily denied economic opportunities. There simply cannot be any comparison to a centuries-old struggle with widespread persecution. Denial of marriage and workplace discrimination clauses based on sexuality (when in actuality, they do very little) can be seen as 'luxury complains'.
So, yes, there are common struggles in both groups. You could write a paper on the commonalities. Howerver, the magnitude and scope of one is such that it even encompasses the other (blacks facing prejudice in mainstream gay culture). Socially, it is not appropriate that the two be compared.