Why not use system_retrieve_file instead of invoking curl directly?

The mechanism to retrieve remote files in FileField Sources is a manual invocation of curl.

Why not rely on the core function system_retrieve_file instead?

I came across a problem with this module that I solved by installing curl, but I had to work through the WSOD first...
drupal_http_request (and therefore system_retrieve_file) does not rely on curl, and therefore would offer compatibility with a greater number of systems.