I think with customers he meant mainly customers who customize and extend the software. Especially if you publish an API and customers can run the software on their own servers you are kind of stuck because you don't know what is being used and how. With cloud based stuff it's a little easier because you can track what people are doing.

Also, Facebook has a history of breaking things for 3rd developers. You can't really do this with enterprise customers who pay a lot of money for your stuff.