Closets were on my mind as I fell asleep last night. I'd been reading a book that contained some vintage (first decade of 20th century) house plans and one thing that leaped out at me was how small the closets were. Alma Boykin's post about cheap clothes helps explain why that was the case. Clothes were once quite expensive, and cheap clothes weren't really prevalent until well into the latter half of the 20th century. As a result, when clothes were more expensive most people owned fewer of them, and required less closet space. I suspect closet space has increased as clothes prices have declined. I offer some anecdotes in support.
The house I spent the first years of my life in was built in the early 1960's, and it had small closets, about the same size as the late 1950's house I bought and live in now. My parent's master bedroom did have a closet twice the size of the ones in the other bedrooms. The single bedroom apartment I rented when I moved out on my own, in a complex built in the late 1960's, had about the same closet space as that first house I lived in. The late 70's era condo my parents now occupy has a walk-in closet off the master bedroom while the other closets are sized midway between the modest closets of the late 1950's and larger ones more commonly seen since the 1980's.
By the time my parents were dragging me along on house hunting trips in the 1980's, walk-in closets had become common for the master bedroom and closet sizes for other bedrooms was creeping upwards as well. The new house they finally bought around 1992 had a walk in closet off the master bedroom and the rest of the bedrooms had large closets, 2.5 to 4 times the size of what I'd had before. The situation was similar in the next two houses my parents moved into, both of late 1990's construction.
Clearly, in my personal experience, older living spaces had less closet space, newer living spaces more closet space. From the recently-constructed houses of friends, I think the trend has largely reached a plateau. However, note the prevalence of various storage locker companies, to allow people to store more stuff that doesn't fit in their house, condo, or apartment. How much of that stuff is clothes? One wonders.