Dear John,
thanks for your post. Yes, we are aware of this, however, similarily to developers of Joomla Core, we do not plan to keep the code limited by PHP4 capabilities.
PHP5 is available already for quite long period of time, so we will start using more of its new features and functions in time.
This means that versions newer that 3.3.0 will not be tested with PHP4 anymore, so there may be more incompatibilities in future. We recomend all users to upgrade their environments to PHP5 or to stick to older versions of JoomSEF.
The show must go on. :-)