There are many forums around where this topic is being discussed. I think it completely depends on the customers requirement, budget and capability to manage the Ecommerce store. We have many clients using
Magento,
PrestaShop,
Cube Cart and many other shopping carts to run their eCommerce websites. We install the shopping cart application and charge only for the web hosting account which starts from just $3 per month. We have also assisted some of our clients with
payment gateway integration and we have not charged them for it.

Hosted eCommerce platform offers limited flexibility, whereas Open source solutions can be customized as per the clients requirement. More features can be added using extensions and custom coding. Both hosted and open source offers good number of features which is more than enough to run an eCommerce website.