Automakers have been carving the luxury segment into finer and finer slices for generations. Territory that once belonged solely to the likes of Mercury, Buick and Oldsmobile is now the fertile hunting grounds of brands from Acura to Infiniti. Thanks to these relative newcomers, buyers without the cash to jump into Bavarian marks like BMW, Mercedes-Benz or Audi can still plant their derrières on supple leather thrones without having to sell the family...