Why are almost all of those light formatters removing your line breaks? Everytime someone mentions some markdown variant (and there are many of them!) and I look up the syntax description, it shows that newlines are being ignored.
If it's trying to be plain text, at least behave like plain text, and don't remove newlines in a shopping list like this (just like hacker news also does with its comments):
-eggs -milk -flour -water
BBCode has it right.
But one of the key features of Markdown (and, indeed, most tech such as programming langauges) is the ubiquity. It's really hard to overcome the fact that almost every platform can export/import markdown.
This is also why the parsing ambiguity/backtracking ends up occurring - humans can read plaintext and do pattern matching with context/attention whereas parsing algorithms have a hard time.