Wouldn't have to be. You don't have to partner with SO to allow folks to ask questions about your product; they just have to be programming questions. Ideally good ones. Also helps a lot if you answer them.

If you want to go further than that, there are various levels of sponsorship possible for a tag, and [internet-explorer] has been sponsored at some level for at least a year. These grant you various advertising and branding privileges, but do not otherwise affect how questions are asked/answered within that tag.

Disclaimer: I work for Stack Exchange but am not involved in the sales or marketing side of things.

True, but Jeff Atwood left SO quite some time ago now.

As catkin has pointed out, Jeff left SE a good while ago. Also his current baby, Discourse [0], is built on Ruby on Rails, Postgres, Redis at the back end and ember.js on the front [1].

[0]: http://www.discourse.org/

[1]: http://www.discourse.org/faq/#tech