Here's a Bell Telephone ad from the April 1960 issue of Holiday magazine illustrated in that pleasant, generic style I always think of as 'retro'.
You know you've seen this style before - its often been used for travel ads - and 13 years earlier in the pages of the same magazine a different illustrator used a similar style for this Union Pacific ad below. Of course there are nuanced differences that reflect some 1940's characteristics and perhaps in a small way, the personality of the artist... but I place it in the same general retro category.
I'm sure you could find many examples of the same style from decades earlier (with subtle variations) - and you still see it being employed by illustrators today. Why, when so many other styles have come and gone, does this one keep resurfacing time and again?
Some years ago I read a fascinating book called "Understanding Comics" by Scott McCloud. One interesting concept McCloud discusses is "amplification through simplification": taking a realistic image and simplifying it - making it more 'cartoon-like' - to amplify an audience's ability to relate to that image.
For instance, the simplified, faceless couple enjoying a horseback ride at a dude ranch (below) could represent a great many people - and therefore a great many people could imagine themselves in the saddle when they look at the image.
"By stripping down an image to its essential 'meaning', an artist can amplify that meaning in a way that realistic art can't," writes McCloud.
The ultimate example of this symplifying process is, of course, the symbols of a man or woman on the door of a public washroom. Stripped of all realistic characteristics, the essential meaning of those symbols is emminently clear to anyone.
While different styles of illustration have come in and out of fashion, the 'retro style' stands the test of time because it fulfills this essential purpose as an "information graphic".
Todays images can be seen at full size in my Travel Flickr set.