Yeah, most men will hit NW2 at some stage, but then most men will go bald to some extent.
The reason NW2 is included on the chart you posted is because it's often considered hair loss. Norwood originally said that NW3 is the first stage of hair loss, but if someone is NW2 and miniaturising, they are balding.
In my view, there's a difference between the mature hairline and NW2. For example, I had a juvenile hairline until I was around 23. I then developed a mature hairline, with no further recession, until around 27, at which point my hairline (very slowly) began receding. I have a NW2 hairline now, 7 years later, at least according to B*sanga.
In reality, most people won't notice the difference between NW2 and mature hairline, it's only people on hair loss forums that debate these trivial issues.