WSO2 Developer studio AS 3.8.0 / Developer Studio EI 1.1.0 - Confused

Am using EI 6.1.1 for which using the Developer Studio EI 1.1.0.

I will be using AS 5.3.0 for which the Developer studio download points to Developer Studio AS 3.8.0.

Download links provide two zip files (as of 12-10-2017):

• developer-studio-eclipse-jee-luna-win64-x86_64-3.8.0.zip
• developer-studio-ei-eclipse-jee-mars-2-win64-x86_64-1.1.0.zip

Questions :

1. Are developer studio/IDE for AS and EI are different?
2. Can one IDE be used for both , AS & EI?
3. Why separate IDEs for each product?

Thanks

Website of wso2.com states

WSO2 Application Server was created as a mechanism to enable sharing of 
business logic, data, and process across the entire IT ecosystem. 
We currently have this capability within WSO2 Enterprise Integrator (WSO2 EI) 
using Apache Tomcat. 

There is no AS in list of products. I think AS server already included into WSO2EI and you can just use 1.1.0 version of Developer Studio(on github.com already available release for WSO2EI 6.2.0 https://github.com/wso2/product-ei/releases).

Documentation is always far behind like half year. I use as well 6.1.1 and have to refer documentation of 5.0.0 version. Just recent time start to appears pages for 6.1.1. That's why you just got stale link of developer studio to download.