So as not to bury the lede (yes that's the spelling apparently):
My question: According to the wiktionary the phrase "safe as houses" refers to something being as safe as investing in house property, and the phrase originated well over a century ago. As an American who has rarely heard the phrase, I am wondering if the average person who uses or hears this phrase would be relatively aware of the etymology, or whether the phrase instead brings to mind a house being physically safe (in relation to crime) compared to, say, a tenement building. Obviously, since it's an idiom no knowledge of its origins is required to use it correctly, but it seems that understanding its etymology might bring a person to use it more often since it makes more sense than a house being particularly safe in regards to crime.
In other words, how popular is the phrase, and is the consideration of its etymology often mistaken, in regions in which it is commonly used.
I should add here that during my research (and about halfway through writing this post, trying to see if I'd heard the phrase in Sherlock Holmes or the few seasons of Dr. Who I've seen) I found out that the rarest incarnation of the good doctor went through this same train of thought as to the etymology. I haven't seen the TV movie or whatever special appearance he made (he didn't play in a live-action season?), and I realize that the popularity of Dr. Who may have brought about a recurrence of the use of the phrase or at least a wider knowledge of its etymology. So perhaps some feedback from a perspective of an audience wider than that of Dr. Who's audience is in order.
Now for some useless garbage background info on why I'm curious about this (tl;dr just skip this):
I am an American and I have never heard the phrase spoken or seen it written by another American, even in TV or movies. The first time I noticed the phrase was a few years ago, online in some ad campaign located in Australia or New Zealand, and thought it might have its geographical center in that area. I then began noticing it in a variety of popular media from the United Kingdom. For the few years I've known of the phrase I've thought of it as "as safe as a house" vs. say... apartments or roads or parks or something. A house didn't seem to be the first place I would refer to as safe, so I wondered if it was a reference to the general safety of houses vs. tenements in the U.K. and I went and discovered the etymology. Then I channeled the good doctor on accident and now here I am.