Yep, that happens as well. In fact in many US states, certainly in California, 2 weeks notice can also turn into collect-your-things-and-go. But this relatively rare, given normal a employer-employee relationship.

In any hire-at-will state, including California, you have the right to walk out at any time just as they have the right to let you go at any time.

2 weeks is just a typical professional courtesy. The employee handbook might state "we prefer two weeks notice", but you don't owe them that.