Depends what you mean by change. If the API changes, all you had to do is to right click on the reference of the API in visual studio and select update. It would fetch the latest WSDL and recreate the code to consume the API. So painless as long as the API is backward compatible.
And on the server side, the WSDL was automatically generated from your code if you used .net, so every time you would update the API the WSDL was up to date.
All that created a lot of plumbing and chatty XML traffic behind the scene, so the underlying exchange isn't as neat as a REST API, but as long as you didn't have to deal with it directly it didn't really matter.