The 90/10 rule

This reminds me of Blizzard's motto of a depth first, accessibility later approach (http://www.gamasutra.com/php-bin/news_index.php?story=10773).

Sure, you can focus on a few features that allows you to cater to your core market. But, what if they outgrow your program? What if they want to go to the next "level"?

A "deep" program like Photoshop allows for that flexibility. A beginner can start off with perhaps the most basic of features but as they become more comfortable with it, at least they still have the flexibility to move on to the next set of (more complex) features.