Currently the BuyNow module supports displaying products and the checkout procedures. If you mark the BuyNow page as secured in DNN, everything is sent via SSL including every single product image!
Typical shopping carts use secure pages that deal with money, including MyOrder (CheckOut) and MyAccount.
I suggest that the BuyNow should be spilt into two modules called Products and CheckOut. This allows the product page to use either http or https while https is only used for checkout with credit card information. Anyone who accepts credit card info over http is definitely not PCI-DSS compliant.
One side effect of separating the modules is that the product page can be cached for increased performance.