It does help Visual Studio and other tooling, but to say it is only "to sell Visual Studio, nothing more" is ridiculous.
This implies that you can't develop large scale apps without type checking, which obviously isn't true.
What's more likely is that Microsoft hires a lot of developers that know the "VS way" of coding, which is using intellisense and type checking, and they made a language that conformed to that. Which is the same thing as I originally said.
productively
You missed the most important word.
As someone who has spent quite some time on Javascript codebases its amazing how quickly things break down when you get developers of different levels working on the same codebase. Optional typing allows a whole batch of problems to be caught way before weird errors/exceptions client-side. Productivity goes way up when the tooling can check basic errors.
(Part of me still wishes Haskell was an option for web scripting but I can dream)
You're not the only one: http://www.di.unipi.it/didadoc/lfc/OtherPapers/Iteroperabili...
(n.b, this is from 1999)
Whether its Google Web Toolkit/Java/C#-to-Javascript generators, Closure templating, Haskell/Clojure/etc. mini-languages, TypeScript, etc. (Job Ad Requirements are one of the great ways to see all this stuff)
When you start working on big applications (e.g. I worked for 5 years on a huge electronic HR application covering everything from timesheets to recruitment to content management to CRM with multi-country, multi-language, multi-regulatory, multi-company, multi-site, multi-thousand users requirements) you realise JavaScript has serious shortcomings...although I still really like the language the tooling and knowledge advances have really, really helped.