y'all have it partly right. we tend to use the flatted 3rd to transition to the major 3rd and more often use a minor pentatonic scale rather than the seven-note scales such you have been using in your examples. this is not to say that octal scales are not used, they are indeed. in fact, there is a formal "blues scale" that is octal. using your key of E examples you'd get: E,G,G#,A,Bb,B,D,E or 1,b3,3,4,b5,5,b7,octave.

Leena, I think the dorian sound that you hear is probably the minor pentatonic scale (although, we start with the tonic and not the 2d as one normally would the 2nd mode--in the key of E it is F# Dorian). the minor pentatonic (in any key) utilizes the intervals: 1,b3,4,5,b7,octave and forms the most common scale used in blues. Leena, your example used C diatonic and the scale formed off of the Bb would be Locrian mode or the basis of a 7b5 chord. the diatonic 2d of C is D Dorian.... or at least that's how we do it here'bouts....

bird

there is also a major pentatonic scale but it is not used nearly as much as the minor variant