There are certainly gray areas here, and legal decisions have come down on both sides. There is the concept of a "stigmatized property," and some courts have held that this needs to be disclosed. An example would be a home in which a notorious murder occurred, or a gruesome suicide, etc.
My sense in your case (consult an attorney for actual legal advice of course), is that you'd have a tough time trying to sue for something like that. It's not related to the property, and I don't think it rises to the level of "stigma" (which would only apply to *your* house anyway).
There's just no way to guess what certain buyers will find objectionable. Even something like a notorious murder can be a gray area. What if it's not in your house, but next door? What about three doors down? Where do you draw the line? Some buyers might be very sensitive to something like that -- others would just toss a throw rug over the bloodstains.
A home for the handicapped is not a methadone clinic or half-way house; in fact I'm sure mental health advocates would probably be offended that anybody's offended :-)
On the other hand, some buyers have tried to sue because the house is "haunted," and that wasn't disclosed. (Proving that anybody can sue for anything these days. There is even a picture floating around the Internet of a for sale sign with a "not haunted" rider :-)
I've personally heard two questions come up from buyers again and again. Some ask "did anyone ever die in the house?" This is generally not something that needs to be disclosed (a natural death, at least) -- and as a practical matter the sellers probably don't even know.
Many homes in Pittsburgh are over a century old, and a century ago most people did die at home -- so if you have an old house, it's likely somebody did die there at some point. I'm not sure why people are so concerned about that -- what about the house that was there before, or the one before that? Over the entire history of a populated area, people have surely died just about everywhere.
The other is "are there any sex offenders on the street?" This is also something that doesn't generally need to be disclosed, unless perhaps it is somehow directly relevant -- for example, if they're moving *because* they think Chester the molestor next door is after their child.
The seller (and agents) are surely not required to keep track of things like that, and absolutely can't do what the buyers really want -- to "certify" or "guarantee" that there are no offenders on the street. All we can do is refer them to the relevant web sites or other government resources, or suggest they call the local police.
The question doesn't make a lot of sense anyway. Not everyone on that registry is dangerous, and just because nobody on the list lives nearby doesn't mean you're safe. They have cars and computers, after all. A neighbor obviously doesn't have to be a sex offender to cause you problems, and even if no offenders are on the street when you buy it, there's nothing to stop them moving in a week later, especially if there are rental properties. (I also doubt the accuracy and completeness of the state-run web site, given my experience of county real estate sites.)
This sort of thing generally falls under the "due diligence" clause for buyers. If whether there's an offender (or jail, or mental institution, or STD clinic) nearby is material to their decision to purchase the home, it's the buyer's responsibility to investigate and answer that question to their own satisfaction.
The bottom line is, sellers can't be expected or required to anticipate and thoroughly investigate anything buyers might be concerned about -- but they *must* disclose any material defect in the property, and *should* prudently disclose anything negative the buyers are likely to hear at the first block party.