Hard Water In Europe
For the most part, many places in the EU and UK have water that ranges from hard to down right solid (*LOL*), even the hardest water found in areas of the United States would mostly be considered soft on the other side of the pond. This is why those using Persil and other European detergents in the States can get by for the most part with a very reduced dosage.
Hard water not only causes problems with automatic dishwashing and laundry, it is very bad for those machines in terms of how mineral deposits can collect and eventually kill the interal heating elements found on all washing machines and dishwashers on the EU side of the pond, hence the built in water softeners for dishwashers. Washing machines get buy with having special chemicals in detergents to prevent limescale formation. Even so many in the UK/EU run "Calgon" through their washing machines (and sometimes dishwashers) to clear out the crud. Once heating elements are attacked by limescale, they are soon not long for the world. This is common and happens to any heating element immersed in water. From hot water heaters, to boilers, to kettles, etc.
In the United States, most homes in areas with hard water, and or high iron content, normally go for whole home water softeners, which is probably the main reason one does not see built in water softeners on American dishwashers.
Regarding phosphates and the EU/UK
Despite the plethora of chemicals designed to replace phosphates, not one single chemical deals with hard water alone the way phosphates can. So while it may not be totally environmentally correct to use tons of the stuff, from a chemcial composition and cost point of view, it certianly is cheaper to use lots of phosphates than have to come up with a chemical cocktail containing several other substances to do the job.