If you choose not to play a card with madness when the madness triggered ability resolves, it's put into your graveyard
New world order In one of his articles, Mark Rosewater introduced us to the New World Order in their design process: They would make sure that the common cards as they are the cards that new players will have the most contact with will never be overly complex: They should be easy to understand and easy to play with, so as these players become more interested and start buying more packs, they will gradually start having contact with rarer, and more complex cards, making the learning curve less steep
Mana doublers are strong enough without a way to spend the mana, which makes this a nasty threat
Save that for Best of One and strange fringe Zombie Hunt-style decks
The fact that its shiny and gold is just gravy
I don't know, but either way I suspect Starting Town will find its way into a many multicolored decks for its versatility