Today. At this very moment.
And tomorrow, without an actual contract, that mechanism could be taken away from you.
Also, not really. There are a ton of biz dev relationships that require more than just an API. Making a public API where "The constraints, the terms, everything is all there" probably isn't worthwhile if you don't plan for many to use the API. In the cruise industry, not many players want access to the cruise API, so they negotiate usage costs and commission individually.
Look at all the companies that are opening up APIs. The New York Times just opened up an API to their entire catalog of articles, definitely wasn't expecting that. These APIs are making the cost of doing business a lot lower.
[1] e. YOU SHALL NOT: (i) use the NYT APIs for any commercial purpose or in any product or service that competes with products or services offered by NYT. (from: http://developer.nytimes.com/Api_terms_of_use)
Yes, APIs will cause the role of Biz Dev to evolve to the next step in it's business function in the same general direction that the Internet has forced sales people to evolve.
I know that biz dev people love self-service APIs - and that they're no longer the gatekeepers of API keys, and can instead focus that time on creating unique partnerships and closing more deals.
Nonetheless, as others have said, APIs facilitate and accelerate true business development.
Yes, anyone can integrate with the easy to use API, but it's bizdev that turns an integration into a channel to acquire more customers. (This may apply more to B2B software than consumer)