I have been trying to explain that phenomenon to people for many years.
The only difference is that I have concentrated on the weight of the atmosphere, whereas these people are concentrating on the weight of the glaciers (ice and snow) at the poles of the planet.

From: http://www.calgaryherald.com/technology/Could+global+warming+causing+recent+earthquakes/4445492/story.html

“The surface of the Earth is elastic. A heavy load such as a glacier will cause it to sink, pushing aside the liquid rock underneath.”

The atmosphere has weight and it is pressing against the surface of the planet much more evenly than the ice cover at the poles, but if the atmospheric pressure decreases then the pressure imbalance on the surface will be somewhat similar to that of melting the ice from the poles.

From: http://en.wikipedia.org/wiki/Earth%27s_atmosphere

“"The total mean mass of the atmosphere is 5.1480×10 to the 18 kg with an annual range due to water vapor of 1.2 or 1.5×10 to the 15 kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27×10 to the16 kg and the dry air mass as 5.1352 ±0.0003×10 to the 18 kg."