In an ever fast paced developing world where new projects and competitors all the time rise and not so old one falls, it requires products to develop and expand outside it's own borders to stay in demand. This is where APIs come in and why they keep being pushed on to existing products. Event old time silo companies have implemented it in their core business products. Although saying they embrace open source, which can be argued, it's their clear strategy in order to stay in business.
As an engineer it's amazing with an API in everything and it gives a feeling that technology is taking us back to the roots of the computers when nerds were hacking with computers in the Homebrew Computer Club, creating computers from raw components or fiddling with toolkits. This eventually led to the start of Apple. With API it is as though we can modify and hack into existing corporate programs and spawn them into new or combined applications fitting a different use case than was originally thought.
Since corporations benefit from this too, it's an easy win win for everyone. Companies should embrace developers and smaller companies to return feedback on which cool implementations they made with the API. It's free R&D (product development) after all.
The future will most likely show us that APIs are getting more standardised for faster implementations and development. Concepts such as REST and OAuth already exists for this matter.
Give ideas a free path and it will be infinite.