In a transmission line, the condition for minimal distortion (caused by the line) are when (R/L = G/C) in the line, right? However, I don't see any reference to that in any application notes or reference guides that I read of microstrips or striplines or high frequency designs. The only condition that I read for the signal integrity is for reflections (impedance matching). Is there any reason for that? Is it just for simplification of the model or I'm just looking at bad quality info?
There is distortion in a line when you can't write the signal in the output as:
V2(t) = K * V1(t-tau)
That means that the signals are not same (without counting the attenuation and displacement of the signal).
There is going to be distortion in the line unless:
a-) Z_0 doesn't depend of the freq. b-) alpha doesn't depend of the freq. c-) V_p doesn't depend of the freq.
All of those conditions are ok when R/L = G/C
If you think about a,b,c : you are changing the characteristics in the line trough the frequency spectrum, so if you are going to change more some frequency components of the signal than others, so that is distortion in the line.
You can see more of the theory of distortion in t.line in this book in section 4.2.