The WP eStore does not do anything with WordPress user. I don’t plan to give eStore the knowledge of WordPress user’s Role management as it falls under the realm of Membership plugin.
As I have mentioned before you can add this functionality with manual tweaks. Basically in the post payment processing script you will have to add in a bit of code that handles this wordpress user creation with the proper Role settings.
The eMember plugin can now be configured so each different membership level can have a default WordPress Role settings. Then when a member signs up in that membership level he/she will have that WordPress Role assigned to him. I have sent you an updated version of eMember so You can see this functionality.