So exactly what is the difference between a “cross platform framework that runs on top of a VM that abstracts the difference in the underlying hardware” in this

So exactly what is the difference between a “cross platform framework that runs on top of a VM that abstracts the difference in the underlying hardware” in this case of cross platform frameworks and a web app where it runs on a top of a browser that serves the same purpose and also abstracts the underlying hardware that has the same drawbacks?