I'm not sure if laundrettes/laundronats really exist in Finland. I live in one of the biggest towns and have never seen one, though it's possible that there are some in Helsinki (and I know one restaurant with a washer and dryer for customers). Most people have their own washing machines and I believe that most apartment buildings have laundry rooms, even though people in apartments are likely to own their own (a washing machine usually never belongs to the apartment, people bring their own). I use the laundry room as there's only room for a tiny washing machine in my bathroom (which is where washing machines live here, unless you have a utility room) and they cost much more and are less useful. Our laundry room's washing machine is quite large and only takes half an hour for a load.
Keep in mind that even in the U.S. laundromats don't exist everywhere. In my experience, when they exist at all, they're located in low income neighborhoods. I haven't seen one in years. Most people who live in single family homes own their own, and people who live in apartments have access to on site laundry rooms.
They are in every neighborhood but the ritziest of the ritzy in my town. And those neighborhoods aren't far from the less chic ones, anyway. There are several on any main street.
It really depends on where you live. In Boston, and I suspect New York City, you can find laundromats everywhere, even in some of the more expensive parts of the city. There are a lot of apartments in older cities that were built before washers and dryers were invented, and there just isn't room for the machines unless you do substantial remodeling, and perhaps some re-plumbing and re-wiring. There are small laundromats on Beacon Hill and all around the Back Bay in Boston, and those are not low-income neighborhoods.
A lot of those laundramats do a big business in doing laundry--people drop their stuff off and pick it up, clean, dry and folded.
Currently, I live in a old city in New Hampshire and there are several laundromats dotted around town, in walking distance to the best neighborhoods. But that might be due to a large university one town over--a lot of the students rent apartments in this city. The laundromats are frequently connected with a dry cleaner.
Even if you have your own machines, it's worth having a laundromat somewhere nearby. For those times when your machines are broken, or you have to wash something large, like a comforter.