Although people make shops with the likes of cubecart, customers do not shop at them.
UTTER UNFOUNDED NONSENSE!! You have statistics or facts to back this up?
I know of CubeCart stores that turn over a couple of million dollars per year. Magento is a cracking piece of software and I am sure it will go far but there is no escaping the fact that right now it is power hungry. I personally don’t see anything wrong with that as long as the hosting solution is appropriate.
Magentos’ target audience such as high end design agencies should indeed provide high quality powerful dedicated or servers within their resources to serve the pages.
CubeCart’s target audience is small to medium businesses and it is a great platform to start on. As all the source code you need is available it is as scalable as you could ever wish.