SSL (Secure Socket Layer) data transport requires encryption, and many governments have restrictions upon the import, export, and use of encryption technology. If Apache included SSL in the base package, its distribution would involve all sorts of legal and bureaucratic issues, and it would no longer be freely available. Also, some of the technology required to talk to current clients using SSL is patented by RSA Data Security, who restricts its use without a
Some SSL implementations of Apache are available, however; see the "related projects" page at the main Apache web site.
You can find out more about this topic in the Apache Week article about Apache and Secure Transactions.