The "public domain" designation has its own problems, nicely summarized on Google Code (https://code.google.com/p/support/wiki/FAQ#Can_I_host_code_t...).

In particular, Dr. Richard Hipp (SQLite's main author) has talked about problems that came up from releasing it into the public domain. He eventually created a second license specifically for companies in places that didn't legally recognize the public domain, and wanted to make sure they were protected from liability.

Licensing is complicated.