I'm not too surprised by this since car ownership is quite expensive over the life of the car. Combine that with the rapidly increasing costs of living, high rents, stagnate wages, etc and things start to give. Not to mention the overwhelming feelings of depression, rage and frustration that comes with sitting in traffic congestion common to East Coast cities for hours on end everyday. I just wish a good, reliable rail network between cities also existed in the US.
In NYC, bike ridership is probably increasing at the expense of subway and bus ridership rather than car commutes (which almost nobody who lives within biking distance of their job does around here unless their job requires an automobile).