Much of the Joomla Platform was written with support for PHP4 in mind.
Given that PHP5 introduced autoloading, many of the classes and
structures pre-date that functionality. jimport provided a Java
inspired solution for registering files to be loaded in a way that
meant that the system was reasonably flexible.
Increasingly we are shifting to using a camel case based autoloader
for new code however as with any project that has been around for half
a decade and two major PHP versions there is a lot of legacy that
needs to be slowly updated.
Cheers,
Sam Moffatt
http://pasamio.id.au