It's not the surface rust that's an issue, the cars available in Ireland are the same cars available here, don't worry.
In cold climates, at least here in North America, roads are often intentionally covered with salt through much of the winter. It helps deal with snow and ice to make traveling safer. But all of that salt that sticks to much of the underside of a car and any exposed mechanical parts, eats away and eventually causes rust much sooner than folks may expect. Heck, the latest and greatest Toyota pickups were just recalled for excessive rusting on their frame when exposed to salt. Here in warmer climates, and even in wetter climates, rust isn't nearly the problem it once was, just as you described. It's common to see decades old cars here with zero rust issues for the life of the car.