Amazon wants more developers to make it impossible to control their devices without an Internet connection, and has added extra APIs for third parties to use.
That's been expanded into what is now the Smart Home Skill API, here.
The idea seems to be that the smart home market, having convinced people that light switches and thermostats are too far away, the next natural step is to convince them that using an app is also too troublesome.
What will “delight” householders, therefore, is the ability to tell Alexa to dim the lights and change the temperature.
There's also a handy bit of forced dependency: third parties have to use the AWS Lambda cloud service to make use of the Smart Home Skill API, because that's where the “skill adapter” runs.
The skill adapter handles requests from the Smart Home Skill API, and communicates with a device cloud. Developers have to support OAuth 2.0 to register a smart home skill.
For developers that need to go beyond the current built-in lighting and thermostat support, there's also a detailed tutorial for setting up custom skills. ®