Can you give an example of a defect that the type system catched? You said typos but that's something JSLint would catch as well so not sure if it's a strong argument.
Misspelled magic strings, which were replaced with enumerations.
We also had a number of bugs with unexpected type use - like a function which expected a boolean but was given a string, or even more common number/string failures.
I've not yet ported my Angular apps to Typescript but I'm very much itching to do so.