Change is coming...and no, I'm not referring to the forthcoming change in Washington. I'm referring to Oracle Application Express.
Since the first supported release of Application Express (Oracle HTML DB 1.5), Application Express has been delivered as a supported feature of the Oracle Database, supporting database releases 184.108.40.206 and higher. So even though Oracle HTML DB 1.5 was delivered as a feature of the Oracle Database Release 10gR1, a customer could actually download it from the Oracle Technology Network, install it in their Oracle Database 9iR2 220.127.116.11, and be in a supported configuration.
For the forthcoming release of Oracle Application Express 3.2, which introduces Oracle Forms Conversion, the minimum database version will continue to be 18.104.22.168. But for Oracle Application Express 4.0, the minimum database version will be Oracle Database 10gR2 10.2.0.x - possibly even 10.2.0.4.