Pressure as a function of altitude
The reported pressures are sea level pressure.  For stations not at sea level (most of them), they can be corrected to sea level through use of the hypsometric equation.  The reason the values are reported as sea level pressure is so that pressure values between stations can be interpreted in meaningful ways.  See for example a typical sea level pressure plot:



In order to produce such a plot, you need pressures on a common reference plane, which is often mean sea level or some other reference pressure level (e.g. 850mb, 500mb, 250mb).  This is why stations report sea level pressure rather than actual station pressure.  This also has applications for aviation, where aircraft operating below a specific altitude (18,000 ft in the US) have to reference their altimeters to a common value regionally and must know the local sea level pressure.