Guinness is sold in bottles and cans with special nitrogen widgets; the taps are specially rigged to have a two-step pouring process; heck, there's even a certificate given to people who learn how to "pour the perfect pint" at the Guinness factory in Dublin. My question is: what makes Guinness so special? Why aren't these tactics used by other stout (or similar variants) producers?
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!
Guinness, and a few other beers out there, are carbonated in part with nitrogen, which has much smaller bubbles. This creates a smoother mouthfeel; this is the "creaminess" that is often described.
The use of nitrogen is probably uncommon for a few reasons. Firstly, there's the added production cost in the bottled or canned product: the widget. Secondly, I would wager that most breweries want the product to taste similar on draught as in a can or bottle, and it's very uncommon to have nitrogen available in a taproom. (You can get special taps which "cream" the beer on the way out, but again, for consistency those would have to be installed where-ever you sell your beer.) So it's something of an uphill battle. Finally, not all beers may benefit from a different type of carbonation than what's prevalent... but of course, that's subjective.
While, as object88 says, it is uncommon for draught beers to use nitrogen, it is becoming more prevalent, though certainly not dwarfing CO2 draught beers anytime soon! So, it is certainly possible to remain consistent from bottle to draught, though it is less common and more costly to do so.
Both bottled and draught beers use nitrogen to add bubbles instead of CO2 on occasion. This is more common with malty beers, say stouts and porters, than it is for hoppy beers. The nitrogen makes smaller bubbles than CO2, and creates a thick head due to the lower solubility of nitrogen in water than CO2 at the same temperatures. This creates the thicker mouthfeel that Guinness (as well as other nitrogenated stouts) are known for.
CO2 will likely continue to be used for most hop-forward beers, since it pushes more aroma out of the beer (including the delicious hop scent!) while nitro is more about the mouthfeel and well-rounded flavor.
A few reasons why other beers don't use the small nitrogen ball devices ("nitrogen widgets"):
Alcohol laws (or FDA or something?) doesn’t allow craft brewers to add widgets/foreign objects to alcohol (cans). Imports exempt?
Not cost effective for small brewers, who are only just able to start affording canning systems.