This is all well and good guys, but the original post asked how to expand out of the pentatonics. An esoteric discussion off all things blue is good from time to time, but what we have here is simple mechanics.
Everyone in this thread is right to some degree. It's all about heart, emotion, letting out your feelings. But simply put, you can't do that without a knoweldge of the mechanics. Ok, you can, but you're going to sit in front of the stereo trying to cop certain sounds while being very frustrated for a long while.
Imagine if you will a person who cannot speak due to a lack of knowledge. The only thing they can do is show emotion. They can laugh, cry, scream, sob, sigh, etc., but that's it. How can that person say what they want to say? How can they convey their thoughts and feelings? They must learn the language. Once they've learned the language, they can more efficiently communicate. But, just because they HAVE learned to speak doesn't mean they stop using emotion as well. They still laugh, and cry, and everything else. But they can now couple those emotions with the apropriate words to convey the exact feeling. Of the two examples, the former is very limited in their ability to convey thought, while the latter has the necessary tools to convey thought and emotion at the same time.
This, I believe, is the thought OSA is expressing. It's also the part that the guys who say "blues is all about feeling" miss consistently. If you 'play the blues', and say it's 'all about feeling', and don't strive to expand your knowledge, you're letting yourself down, taking the easy way out, and are a prime example of why naysayers maintain "Blues is easy". They're right, of course. That part of blues is easy.