Upon careful inspection, you are correct: your group permissions are the problem. Additionally, you *may* be misunderstanding whats going on with unix permissions.
The owner (rwx) is www-data. You are a member of the group www-data (r-x).
Again:
The directory's OWNER, is the user www-data, the directory's GROUP is the group www-data.
This does not mean if you are in the www-data group, that you are the owner. The naming here is confusing and I think thats where you are getting hung-up.
Imagine if you changed the owner to 'bruce080'. This would not affect anyone's permissions in the www-data group, because www-data doesn't 'own' the directory, 'bruce080' does.
The short answer is you need write permissions for group.