It’s misleading to take this headline and not actually read the document and notice how few these differences are.
Observable cells are basically Javascript, with a small handful of additional conveniences (most importantly: they can reference other cells reactively) which make a huge improvement in the notebook context, and make Observable significantly more pleasant than any other notebook environment (Jupyter, Mathematica, etc.).
Javascript libraries and code snippets can be used as-is in an Observable notebook, and anything in Observable cells can be straightforwardly ported to vanilla JS at the expense of a bit of effort and slightly uglier code. (Or the Observable runtime and standard library can be used directly externally.)
Observable cells are basically Javascript, with a small handful of additional conveniences (most importantly: they can reference other cells reactively) which make a huge improvement in the notebook context, and make Observable significantly more pleasant than any other notebook environment (Jupyter, Mathematica, etc.).
Javascript libraries and code snippets can be used as-is in an Observable notebook, and anything in Observable cells can be straightforwardly ported to vanilla JS at the expense of a bit of effort and slightly uglier code. (Or the Observable runtime and standard library can be used directly externally.)