Kobo does not make any of its Writing Life authors sign exclusivity deals or retain the copyright for self-publisher's works. You will be free to publish your books on any other site or in any other store you wish.
We are determined to making it as easy as possible for authors to publish their books with us and giving flexibility and control to the author is a big part of making that a reality.
While we don't like to force an author's hand where having an exclusive title on our platform means there is additional access to further tools (like one of those other big ebook retailers makes a habit out of), there might be some terms and conditions at Kobo that suit your needs better than those other places.
For example, Kobo Writing Life doesn't have a 70% price cap at $9.99. So, for creating more expensive books (such as box sets) in a way that offers your readers a good deal but without crippling your ability to earn a decent income from those sales, you might just consider publishing that title to Kobo and not, perhaps, to Kindle. (Not that we require exclusivity, just that it might make solid business sense for certain titles)
As mentioned above, we're here to provide you with free tools to operate your writing/publishing business. When we build upon and improve features within Kobo Writing Life, we do it with the intent that all users can take advantage of those tools.