better at parsing the Penn Treebank than the best
natural language parser for English on the Wall
Street Journal
I'm pretty sure "the 20 year old Penn Treebank" and "the Wall Street Journal" are referring to the same dataset here. In the early 1990s the first large treebanking efforts were on a corpus from the WSJ, and they were released as the Penn Treebank: https://catalog.ldc.upenn.edu/LDC95T7 People report results on this dataset because that's what the field has been testing on (and overfitting to) for decades.(I worked on a successor project, OntoNotes, that involved additional treebank annotation on broader corpora: https://catalog.ldc.upenn.edu/LDC2013T19)