Mathematically 100, 125, 150, 200 make more sense than 135 and 180. If the arguement made here stacks up then why have a 180 & a 200 and why jump from 135 to 200 if you exclude the fact the 180 is a macro lens.
Depending on what kind of math you follow.
In this case, the numerical focal length matters less than the Angle of view.
The AoV for the commonly used telephoto focal lengths are (horizontally):
100mm: 20 degrees
135mm: 15 degrees
200mm: 10 degrees
400mm: 5 degrees and so on.
That is why, 135mm makes sense and not 125 or 150.
Mind you, lenses at some focal lengths are probably more optimal (in terms of price and performance) to design than others- that is a more important aspect for designers than keeping symmetry in numbers.