Compact cities tend to be more walkable and transit-friendly, because in a dense, compact city, more people can live within walking distance of shops and transit stops. Paris and Amsterdam are more dense than most of the United States—but not outstandingly so from my New York City perspective. Paris has about 55,000 people per square mile—more than New York City as a whole but less than Manhattan. Amsterdam is much less dense, with a little over 12,000 people per square mile- not many by New York standards, but still comparable to transit-friendly cities like Chicago and San Francisco. Even in Centrum (the most dense of Amsterdam's boroughs) there were only 28,000 people per square mile, only slightly more than the citywide average in New York.
In both cities, I stayed in transit-accessible suburbs rather than in the touristy, expensive core. But even in its suburbs, Paris seemed to have a high diversity of uses; it was very common to see shops on the ground floor of residential blocks, even in suburban Levallois where I stayed. This diversity makes it easier for people to walk to shops. Similarly, Centrum is mostly mixed-use. The post-World War II, suburb-y parts of Amsterdam, by contrast, do have areas dominated by residences. But in these neighborhoods, as in 1920s American streetcar suburbs, a commercial street was usually just a few blocks away.
The biggest difference between these cities and American cities, however, relates to design. Even in my Manhattan neighborhood, most street space is reserved for moving automobiles. By contrast, in Paris and Amsterdam there are fewer automobile lanes and more space for pedestrians (and, in Amsterdam, bicycles). In Levallois, I stayed on a two-lane street with one lane for parked cars and only one more lane for moving cars. Amsterdam had far more bike lanes, but also seemed to have a lot of one and two-lane streets. Narrow streets have obvious benefits for pedestrians and bicyclists: traffic is slower, and when you cross the streets you have fewer lanes to cross.