What makes a bedroom?

Another bout of snivelling colds and hacking coughs has us torturing ourselves watching reality shows and HGTV. It's about all our feeble brains and even feebler bodies can cope with. We expect nothing from this TV except entertainment but occasionally we come away with a piece of knowledge that we would be unlikely to glean anywhere else.
Watching HGTV's "My House Worth What?" over the weekend we heard a realtor say that in America the legal definition of a bedroom is a room that contains a built-in closet! We were pretty much astounded by this because we'd always assumed that a bedroom is any room used for sleeping. It also means that of the many houses I have lived in, only four had bedrooms. The majority were either too old to have built-in closets or were in countries where this was not an issue. We just purchased wardrobes or armoires to hang our clothes in and put these in our "bedrooms". We knew no better.
So I checked the internets for an online definition. Three online dictionaries described it as a room containing a bed, while another gave this definition that is at once vague and overly precise. "Any habitable room that can be used for sleeping. This typically includes, but is not limited to, a room with a proper escape window and one in which there is a closet or a door OR a closet or a door could be reasonably installed. ...". I don't understand why it would be either a closet or a door or the possibility of either that defines a room but I know if I had to choose between the two I'd go for a door every time. Because otherwise it's a box that I can't get out of, no?
Of course I couldn't leave it there. I had to know - what makes a bedroom, and I found another definition in the San Matteo, California town code "an enclosed habitable space" that is designed primarily for sleeping and contains at least one window. State building codes require that a bedroom must be a minimum of 70 square feet.
It's all very confusing but I know one thing: Most of the built-in closets I've seen have the ugliest doors* and I'd rather have a sleek modern PAX wardrobe from IKEA or a beautiful old armoire any day.

* If all closet doors looked like this I'd take that back!