[eluser]Michael Wales[/eluser]
This has been discussed over and over and over and over and over...
The problem lies within hosts - they consistently offer a deprecated version of PHP to their customers. This has absolutely nothing to do with EllisLab. The Lab runs a business and that business is the release of PHP software.
What if EllisLab decided they were only going to sell ExpressionEngine to people who wore green pants? It wouldn't really be fair and they would cut out the majority of their customer base (I, for sure, would never be caught in green pants).
When more hosts switch to PHP5 only - and it makes sense to move to PHP5 only - then EllisLab will do so. Until then, it's simply not going to happen - there is no logical reason for it.
Sure, code could be refactored and make use of some pretty cool aspects of PHP5. But, no one at EllisLab will get paid for a few months because only 30-40% of their customers can run the "new and improved" ExpressionEngine. EllisLab starts firing people, CodeIgniter loses focus because there aren't enough people to work on it. 6 months down the line EE isn't bringing in enough money and EllisLab's assets are liquidated.
Rick then moves on to creating AdSense arbitrage sites. Derek Jones moves on to an executive position at XBox Live. Derek Allard switches to ruby and starts writing his own framework. CodeIgniter dies.
Let's stick with PHP4 for just a bit longer guys... if you want CodeIgniter to be PHP5, start talking to hosting providers.