[eluser]TheFuzzy0ne[/eluser]
I agree, it shouldn't be the case, but sometimes the API must change to encompass new ideas. Rule of thumb is not to upgrade CodeIgniter unless you have to. If your app has been built with a particular version, and it works, you should stick to that version of CodeIgniter, unless there is a specific feature or bug fix you need for your app, in which case you need to
upgrade your app too. Contrary to popular belief, CodeIgniter has not necessarily been designed to be backwards compatible, although it is in most cases.
I am quite sure that CodeIgniter will change again, to allow us to extend the base core libraries easier, such as the database library for example. You can't always get everything right first time, and sometimes making something backwards compatible is just too hacky, which is when a new version is needed.