If I wanted to simplify this, I'd say that this was a programmers vs customers conflict of interest. Programmers tend to use new features for many reasons. Because the new features can improve the appliation speed, or they make the application more reliable or extensible, or they ease the development task,or even merely because they are new features and programmers want to try them out. Whether these new features add something from the customers' business point of view, that's the question.

The extreme case perhaps can be seen between 4.x and 5.x upgrades, or big features in 5.x series such as unicode support. If the customer needs unicode support then choice is clear. For me, it's hard not to move to Perl object oriented and leave 4.x behind.