title_body: Why does Guinness have a special pouring process / bottle, while other stouts do not?
upvoted_answer: Guinness is "carbonated" with nitrogen, where most beers use carbon dioxide. This requires different hardware, bottling equipment, etc.
  
  If you've ever witnessed the appearance of a perfectly poured Guinness, and paid more than $5 USD for it, you'll understand why. It's partly about presentation. As one of the oldest beers on the market, it requires us to jump through some hoops to ensure we are enjoying it correctly. In short: I think it's mostly marketing!