I don't understand your concern, since you need to actively shift the bike into a specific gear, it doesn't default to a gear. You would have to remember to shift down when you stop no matter how the derailleurs were configured.

But, to answer your question:

1) Actually, the front derailleur will shift to the small chainring if the cable is released.

2) The reason the derailleurs default to the smaller sprocket is because it requires more effort to force the chain onto a larger sprocket than it does to drop it to a smaller one. A small spring mounted in each derailleur provides sufficient force to drop the chain from large sprocket to small sprocket. A much larger spring would be required to go the other way, which would a) be heavier, and b) be harder to pull against when making your shifts the other way.