This definitely depends a lot on the airport and distance you are traveling. San Francisco to New York, Los Angeles to Chicago... America is too big for land to be faster. Stuff is a closer in Western Europe.
You are right. The example I gave is probably a bit skewed to faster travel times. If I had chosen say Barcelona to Moscow, times would have been a lot different.
The other difference is that the trains in western Europe are much faster than their US counterparts as well.