We're all really saying the same thing
SDKs? Where we're going, we don't need SDKs
Because the REST API is the driving force to the ArcGIS development, you could theoretically write all your applications from scratch against the API without using any ArcGIS SDKs. Sometimes this becomes necessary when the features in an SDK may not be up to date with the latest features of the REST API. The more familiar you are with working with the REST API, the easier it is for you as a developer to overcome these hurdles.
Need to interact with ArcGIS Services in a server side application? You can talk to the REST API directly just like this ArcGIS partial class library does. You can run your queries, customize the results and output the information as needed. You don't need to be limited to official SDKs and tools, the REST API is there for your abuse use.
Have fun with it
So go on, give it a shot. Next time you find yourself limited by the SDK of your choosing, try to see if you can interact with the REST API directly to get the desired results. Up your game and get things done.
For more tips and tricks, be sure to check out my geodev blog.