[tetraodonpuffer]

API consumers might also not be very flexible when it comes to adapting to API changes: some might have developed fragile/inflexible code that will go up in flames if you even add a new field to an object (leading to support calls and escalations), this is why depending on your domain you might need very strict versioning requirements.

Some APIs will not change a version number even if new objects/fields are added, others will, it really depends by what space you are in and your customer needs and it should be taken into account when designing your API.

[smizell]

I think you are right here. It takes two to tango, and if the clients are tightly coupled to the API, the best intentions for evolving slowly will fail. :)