Why so many assertions? Simple `assert` not enough?

I'm starting Rails, and I have no idea why it gives us so many assertion types. Isn't simple assert enough for most (if not all) of the patterns?

For example, I can't find a reason to use assert_equal - what's the point of using it if you can do assert expected == actual ?

In fact, it's probably not about Rails actually but about all the test frameworks following JUnit's style.