southwest has twice the number of a/c but you don't hear them constantly asking for weather or higher levels, same applies to LH or other big outfits that plan their flights at the optimum levels and use acars to gather info without congesting the air ways.
That's because in the US pilots from every form of creation can obtain wx via FSS or Flight Watch... something I availed myself, because I was too damn lazy to use ACARS. Too bad in Euroland, Zurich is one of the only stations one can obtain weather at destinations and conditions around the region.
On my transcon flights I've heard numerous carriers request higher and directs, including SW with their twice as many aircraft as FR too.