Alex, there are two different classes of patterns under discussion. The type you are referring to is what would fit a specific song, and by extension a number of individual songs which can be grouped together as sharing that pattern, using the same chords.

When I talk about a "very broad pattern," it is most clearly seen from the numerical point of view. It is not to say that a song that goes G-Em-Am-D can be played with G-E7-A7-D7, or vice versa. It is rather to point out that a great number of songs which go from G to E-something (major, minor, seventh, whatever) will then go to A-something and then on to D-something. Whether it's G-Em-Am-D, G-E-Am-D7, G-Em-A7-D, etc., what these specific patterns have in common is that they go through the circle of fifths (more info here and here and here) in the same way. There is a fair amount of significance to that in the big picture of various sound relationships in music, hence there is some value in seeing it as a broad type of pattern. It is, as you note, to be distinguished from a pattern or sequence of specific chords that would be used in a particular song.