Shopify constantly seem to be pushing new ground, although I find it hard to imagine a store on that platform turning over $1,000,000+ just seems to limited unlike Magento.
I work with ATG, Hybris and IBM WebSphere mainly. These are the biggest players in ecommerce and some of the biggest brands with massive turnovers use these platforms.
Magento is seen as a bit of a joke among big enterprise ecommerce players. The kind of thing will a low entry barrier and with a userbase primarily made up of small retailers.
However, I would love to start my own ecommerce agency and the low barrier to entry could make magento the perfect choice for me. I'm not sure if any retailers actually spend serious money on it though, unlike the 3 big players I previously mentioned.