The forums that are labeled "You must be a XenForo customer to post in these forums. Ensure your account is listed here." are for licensed customers only. Attachments in those forums cannot be downloaded unless you are a licensed customer. The screen shots you are referring to are probably attachments and therefore cannot be viewed if you are not a licensed customer.
Yes, however, from a pre-sales standpoint I'm not sure whether to buy Xen or not. I have pretty specific needs and need to have a certain style theme with certain plugins, hence why I needed to see the screenshots.