I guess it's all about presentation. The Slanket actually seems like a good idea, while the Snuggie is creepy.
Yeah, the Snuggie commercial has all the stupid people not knowing how to use a blanket, not to mention showing people wearing what is basically a long coat backwards in public.
Meanwhile, today I celebrated my first day of winter break by lying in bed all morning while playing Animal Crossing and Persona 4, and I'll be damned if a Slanket doesn't seem like a better idea than my blanket in retrospect. (Luckily, both the Wiimote and PS3 controller work just fine under my comforter. I can't use the Wiimote as a pointer, but it worked for AC well enough.)
Is there a term or phrase to summarize that? I've grown more and more amused at the technique of infomercials where they show, in black and white, people flailing about unable to use something like SCISSORS, possibly injuring themselves in the process, with downright nauseated expressions on their face. Bonus points if they actually THROW the "ordinary item" away in disgust.
It's hilariously stupid and the fact it's such a trope is kind of amazing since, yeah, as you mentioned, it leads to I CAN'T USE THIS BLANKET.