Heh, 90% of all my Subdivison street plans for the past 30 years are at 40 scale....
Of course, for the past 5, or so, years they've been going to 30 and 20 scale......between the miscellaneous crud that the plan checkers just HAVE to have that only takes up space and my tired eyes that don't want to focus on small things I NEED more space between the linework......
As for the default, I dunno, but it it will give me something to investigate this wet weekend.