To be clear, I definitely agree that retailers on the scale of Walmart, Target, Home Depot, Macy's, etc. (probably M&S then? I don't know Britain well) probably have the budget and justification to in-house the ecom website if they have the appetite for it, and indeed, given how unique their needs are are relative to the median site served by the likes of Shopify or even the average customer of the "enterprise" platforms like ATG... they're likely to be able to see a positive ROI on it, unless they screw it up big time.