Perhaps the philosophy of commonmark should be less about what every other parser is doing.
And more about, what would be the Common Expectation of users when writing markdown.
In other words. The aim should be more about a Lightweight Markup Language of No SurprisesTM .
This is because the biggest attraction that made iphone beat most other more feature rich competitors, is that it ‘just works’ from the average user experience.
tl;dr: Be common in user expectations. Not in the Status Quo