Plug-in development

Hi, 

I'm researching about the plug-ins development and I've seen in the documentation that a local installation of Appian is required to develop and test any type of plug-in. For instance, in this page it says the following: 

"In order to individually build a custom smart service plug-in, a licensed local installation of Appian is required. Appian Cloud customers who have a local installation must develop and test the custom smart service locally and coordinate with Appian Technical Support to deploy it on their site."

Why is a local installation necessary? Is it because the Appian JAR (<APPIAN_HOME>/_admin/sdk/appian-plug-in-sdk.jar) has to be added as an external dependency in the IDE? The JAR file can only be obtained from a local installation?

Thanks in advance