[edit] BTW there is a legend here that in Siberia people actually keep a fire under engines to warm it up. I even found a photograph of lorries to support this: http://www.marxists.org/history/ussr/art/photography/workers...
Not sure if I would do it with gasoline engines. With diesel engines it's quite understandable, particularly if you have summer-grade diesel fuel that starts to congeal in -15C.
These areas, in Siberia and northern NA are much colder at times, even when they aren't within the Arctic Circle, so their situation might be considerably different.
Now if you live in Kiruna or Luleå or so, things are a bit different...
[edit] It is true that modern cars don't need a block heater to start up successfully, but heating the engine before starting reduces fuel consumption and emissions radically.