Unfortunately we can't allow access to the robots.txt file> The reason is that there is a universal robots.txt file managing the software across all stores as a default.
This means the file manages page extentions that are generic in the software, such as search pages or product filtering pages and relays to search engine that they should not be indexed.
However, in your Google Webmaster Tools account you are able to manage the file directly for your domain. You can find the list of page extensions to edit under the link on the left menu called "crawler access".
