Firstly, the times are not similar in each direction, since one way is in a jet stream and one is going against the jet stream.
BTW, guess what is responsible for the formation of jet streams... ...That's right,
the earth's rotation!
Today, with relatively accurate prediction and mapping of the jet stream, it is possible to flight plan based on jet stream prediction, but many more planes fly outside a jet stream than within one.
Actually flight planning around jet stream predictions can increase a commercial jet's ground speed by nearly 50% under ideal conditions, saving huge amounts of fuel over time. Conversely, an airline will go out of its way to avoid coming near the core of a jet stream on east to west flights.
But they are far from ubiquitous, and the core, occasionally with speeds over 250 MPH, is pretty small.