Understanding papers depends on what your field is.

For example, I'm interested in optimization/signal processing/machine learning and finishing up my education. In the related journals I can barely understand the notation and miss the higher level concepts.

On the other hand I'm taking a class that required me to read a journal paper written by the professor. It was strange: I could understand it. I followed it and most of the finer details too.

I would say that OPs statement is true: 99.99% of papers published by math profs are incomprehensible to almost everyone. Not only do they use foreign notation there's also a lot the don't say because it's assumed the reader knows enough to prove it -- hence "left as an exercise for the reader..."