Joke title aside--I will edit if anyone complains, but I thought it was funny--he's complaining that nobody seems to remember there are any specifications for motherboard size beyond ATX, and so motherboard and case manufacturers basically make up their own (EATX, BTX, EEATX, etc) and then, since they're not referencing actual specs, they have to say what the maximum board size is. This bothers Steve enough he made a 22-minute video. Basically, most cases describe anything bigger than 9.6x12" as "eatx", but since they're not actually referring to a specification, it might mean 10x12 or 10.5x12 or whatever.
3/4 of the way through, he tells a story that probably explains what set him off, but doesn't mention that. Every time someone sends him a motherboard bigger than ATX, he has to go sifting through a pile of cases to find one that actually fits the board. (I've seen Tom's Hardware rant in passing on this before.) I would imagine that gets tiresome after a while, although since he has a database of inventory, maybe he could add an extra field to describe "maximum motherboard size" on a case to save himself time in the future.