Comment is useful, the code above that comment must be php4 compatibel, so that when someone loads piwik on php4 it displays nice error message rather than parse error.

@mattab just a wow for that...since PHP 5.3 is EOL, Piwik still cares about PHP4? Again wow

@ThaDafinser It is solely to provide an error message and show the user that his version of PHP is not supported. We care about 5.3 since ~50% of users still use that version of PHP.

Agree with mattab. It seem, there is still 2% of PHP 4 users:
http://w3techs.com/technologies/details/pl-php/all/all
If a message require explicitly PHP 5, they will not lose time and we can hope they will upgrade. Else maybe they will not even understand what happend and why Piwik does not works.