Actually, its not so stupid. If they let home business buy things like cell phones or video game consoles, it would put major retail stores out of business. Home business can charge much lower fees than retail stores. Retail stores have to pay overhead, employess, insurance, etc.
To the manufacturer, retail stores are their bread and butter. So they won't jeopardize the relationship between retail.
Yes, it's stupid. But its how manufacturers keep their business afloat. To the manufacturer, it's business as usual. Home business don't bring in the business that retail stores will. Plus it can narrow it down to who screwed them over, if there is fraud going on when they only sell to retail stores. If they sold to home business as well, it would be much harder to track down con men, which would in turn give the manufacturer a bad name.
I hope this explains it to you Crakah

Take care