The reality is that a lot of code is written by average programmers trying to get a lot done in a hurry. A static check is the difference between a subtle bug making it into production and a helpful, specific error at compile time. Most projects do have bigger problems than static or dynamic typing but static typing is even more helpful there than it is on projects staffed only by top-flight coders with plenty of time to do things right.
In the three years I've been doing consulting work I've had to clean up a lot of legacy code. Believe me, people do make these mistakes in real-world code all the time.
