Leitwolf -- I do agree that we have a lot to figure out still regarding HIV/AIDS, and I suspect that retroviruses in general still have a lot more surprises in store for us generally. Some groups of people do seem to have relative immunity to it and have been studied some, and any disease involving major immune dysfunction is interacting with a whole system in the human body that we've still got heaps of studying to do; actually, untangling some of the details of immune system connections, including autoimmunity, is one of those areas where I expect we're in for some major, understanding-shaking discoveries in biology over the next century.
I don't think any researcher in the field would argue that some people don't have more immunity to HIV infection than others.
But it isn't the case that some level of natural immunity against initial infection -- almost any disease will involve some individuals who are more resistant -- means that infected individuals can be healed. I _don't_ see any real evidence that anybody has totally cleared the virus after having been solidly infected, but I'm not closed to the possibility, I suppose. I have known people who have gotten viral loads down to basically undetectable in blood, but have had it come back over time. Immune activation is certainly there, but immune activation in itself doesn't mean the immune system is going to successfully clear anything, particularly with a virus that specifically targets immune processes. What evidence points to now -- and there's lots of it -- is that HIV is a lifelong infection that can now often be brought under some control via treatment. Lifestyle and dietary changes are vital factors in the development any major illness, really, as immune system function does seem to be pretty sensitive to all sorts of factors -- sleep, food, stress, so on -- but these are about controlling symptoms and maximizing the body's ability to handle the virus, not about clearing it.
And I can't agree with your point about HIV not "making it" if it's so lethal. It can take years for some people to develop particularly major symptoms after contracting HIV, plenty of time to continue spreading it through the population. Major disease events with very high death rates are really not that uncommon in the history of any species, they're a fairly common sort of an evolutionary bottleneck in everything from small populations to global species. For the most part, species gain immunity to stuff through just this process -- a huge proportion of the species dies off, those lucky ones that are left are the ones with some level of protection against the pathogen. Of course, then the pathogen mutates to survive, too, so it's sort of a constant arms race. In the history of life, major near-extinction events from disease are not uncommon at all. Evolution can be slow, but it can also happen very quickly in response to a major new selection factor, and losing 90% of a given species to a new variant of something would be no huge shocker, in historical/ecological terms.
That's not something we can or should accept in modern humanity, of course, but the trick for viruses, particularly those that require close contact, is simply to not to kill so swiftly that they can't be spread. With some people living with HIV for years before they get terribly sick, that's not a problem for this particular virus, and with infection requiring very close contact, the likelihood of finding new hosts continues for it for a long time (it won't sweep through on nasal secretions in a couple of years like, say, the flu, any particular strain of which may flare up, be exposed to 90% of people over three years or whatever, and then die back down as immunity is gained). Unchecked, it would still take a long time to work its way through the human population -- if it hypothetically did so, it's not unlikely that we'd see a huge number of deaths until those most genetically prone to infection had all died off, but that would take many decades, at a minimum, to unfold.
I'm not all that theoretically bothered by the fact that XMRV is there at a fairly high rate in controls; we don't know what it does over time or how it interacts with other factors. It could mean that it doesn't cause symptoms of disease unless it interacts with some other factor, potentially something like a genetic susceptibility, potentially some environmental thing. It could mean that it has a long latency in some people, too. A lot of diseases can have hosts that act as carriers, never really developing symptoms but contributing to the spread. And sometimes, a microbial pathogen can be no big deal for most of the population, but trigger lifelong autoimmune problems in a certain group, say, or cause permanent damage to the brain or whatever.
Lots to learn, lots to learn.
