... You may wish to re write the as it is vague, yes the flat 3rd in in all three minor scale but it is not the key or guide tones.
Quite right.
All three of the 'minor type' scales are considered 'minor' because of their flat third.
Their distinctive character / sound is due to the other notes you mention ...
Dorian is 'minor' (because of the flat 3) with a key note being the flat 7
Phrygian is made distinct by the flat 2 and flat 6 aswell as the flat 3 and flat 7
Aeolian is the 'natural minor' ... the minor scale that people generally refer to as
the minor scaleLocrian has many flattened notes that give it its character
The b2 and the B 6th are keys tones of a minor scale that sound like your cold.
The Phrygian!! Fridge - ian!!

Some should contact Justin and see why he things that it cool to to add these 6 and 9 and call this the Dorian mode.
Like Dorian my waiter it just something he made up 
He is bending his own rules i believe ... just to give folk something different to think about.
Justin in general says learn the major scale then learn the modes (which means Dorian comes after the major scale is learned).
And yet he is suggesting that using the minor pentatonic with a couple of extra notes added leads to playing using the 'Dorian approach'.
This is slightly contrary to his learning philosophy I think ... but I also think I know why he does it and why it works.
I think he does it to give people that went doen the road of blues playing with minor pentatonic before going down the major scale road a little something to 'spice up' their playing and give them an extra dimension.
It works because the A Dorian scale is exactly the same as the A minor pentatonic with the 6 and 9 added.
A minor Pentatonic:
A, C, D, E, G
1, b3, 4, 5, b7
A Dorian
A, B, C, D, E, F#, G
1, 2, b3, 4, 5, 6, b7
8, 9
All theory I know suggest that Dorian is the minor mode which would not have a Dominate chord as the one.
It works because of the flat 7 and the flat 3 creating that blues tension against the Dominant chord.
... Does those notes sound good yes the blues is kind of base of a feeling more than theory
There we are ... agreement ... it sounds good ...
And this also goes to that current thread on how much theory to learn .... you can analyse stuff ... but if it sounds good you don't need to ...
...and the feeling I get when I look too the west and the spirit is crying is half Dorian ,Half Aeolian, that b 6th in the solo removed the mist and made it clear.
I disagree there ...
The solo is fully within the A minor pentatonic scale .... apart from one note ... the note being F ... that Jimmy plays over the F chord ... it is indeed the flat 6th and for that brief moment you could say he is then playing a part of an A Aeolian scale (but without the 2).
Because there is no 2 and 6 I don't think you would describe it as A Dorian.
[mod edit - for a continued discussion on the stairway to heaven & its scales see this thread]http://justinguitarcommunity.com/index.php?topic=27950.0