Well, The SSL bug only affected Mavericks. Additionally, I don't think we know if the security updates released for mountain lion and lion also affected Snow Leopard. And if it did, well, Apple moves quicker than Microsoft does anyway with new OS release every year.
If there are still people running Snow Leopard, either they have an old computer that is more than 5 years old, or they specifically don't want to upgrade to Lion. For the former, Apple knows most people will have upgraded their old computers by now, or will soon in the future. For the latter group, most know what they're doing by not upgrading.
Snow Leopard is 4 years old. And the last update for it was September 2013, just 5 months ago. It clearly was Apple's XP, if you will, and the longest supported out of all releases, I think.