It's always been the case that some disorders are cooler than others, just like some illnesses are. And for much the same reason.
I.e. (and I'm talking stereotypically here, not accurately) aspergers tends to cause social awkwardness - they willl still socialise but in sometimes slightly inappropriate ways, they can be hard to talk to, and they can worry people (i.e. avoiding/constantly holding eye contact, not picking up on signals, odd conversations.) Sociopathy leads people to more often avoid socialising - so they are considered enigmatic, not awkward. Also, sociopaths are more often capable of understanding societies unwritten rules, even if they don't follow them. People with this type of anti-social personality disorder often have a lot of charm. Anti-social personalities also seem to have more control (they can have charm, or manipulate, so they can choose to be social) whereas aspergers do not - they are unable to socialise without special teaching. Being out of control like that is not as glamourous as appearing not to care.
Also, Aspergers is not an antisocial disease. It's a developmental disorder that effects your ability to socialise with others. Whereas sociopathy is a personality disorder (technically it's not anti-social personality disorder). So Aspergers is more likely to be combined with other developmental or learning problems (especially language processing) which, again, is considered either strange or looked down on. Anti-social personality disorders are not, as much, so these people hold their own in their peer group better, so have higher percieved status.