eZ Publish requirements page points PHP 5.3.x, or PHP 5.2.1 -> PHP 5.2.17 as requirements for supported and approved platforms.

On the other hand, Requirements for doing a normal installation page brings the following information:

Note that it is strongly recommended to use the latest version of the 5.x branch, which is PHP 5.2.17 at the time of writing. The reason for this is that eZ Publish runs faster on PHP 5.2 than on PHP 5.1. In addition, some extensions may require PHP 5.2

The latest PHP version so far is PHP 5.5.4.
eZ Publish already has incompatibilities at PHP 5.4 (See EZP-18259).

The Requirements for doing a normal installation page should be updated to remove the information about being "strongly recommended to use the latest version of the 5.x branch".