understanding the php 5.2 requirement

I had a similar problem due to using a server that can't run php 5.2 - I took the php=5.2 line out of filefield.info and it seems to be working. However, I wouldn't guarantee it would work in all circumstances so I'm doing this as an interim measure and will move the site to a server running 5.2

+1 for a developper answer ! Please :)

While still in 5.x.-2.x-dev, this dependency apparently has been removed from the D6-Version.
I couldn't find any dependencies higher than PHP 4.0.7 in both, the D5 and the D6 version of the module.
Can someone clarify?

Where do you see that ?
In 6.x-3.0-alpha5 and 6.x-3.x-dev there's still the PHP 5.2 dependency in filefield.module. It's just not written on the module's homepage in the D6 section.

You're right, I checked for hook_requirements(), which is gone. Now it is defined in the .info.
Nonetheless, reading the code (5.x-2.3) I didn't find any reason why it should require php > 5.2.

I no longer remember the particulars... I do recall issues with objects passed by reference into functions losing references to object type properties. A functioning recursive mkdir, and several small bug fixes between 5.1 and 5.2.

The real primary reason, I run php 5.2 and I'm not downgrading to support <= 5.1.x. when you're a module maintainer and you have multiple versions of multiple modules for multiple versions of Drupal, you can decide which versions of php you want to support and require.