Google may start charging for API use. At this point, most Google APIs are doled out on a limited basis and their limit puts a real limit on the functionality of the service using them.
Some people see the coming charges as a barrier.
From MediaPost:

Previously, Google made its API available for free, but [...]

You know that auto-pinging brings you traffic.But, did you know your content is indexed when you auto-ping?  In other words, you get:

more weight in the search engines
more chance of having the content the searcher is looking to find

Your content will resonate very fast.