Currently, most hosting providers offering a shared hosting do not include support for PDO in their PHP5 enabled web servers. That means most web developers are stuck with the old database functions and can't migrate to PDO. PHPPDO makes such a migration possible by providing a PDO-like API interface over the old database functions. After using PHPPDO, a migration to PDO afterwards is a matter of changing a single line of code (this can even be automatic, when the script detects PDO).
