Perhaps in the U.S. this is true with the standard issue low watt phones and lousy cell infrastructer.
Would you like me to give you a ring from the tunnel under the Hong Kong harbor or from inside the elevator of my building? Signal at 5 bars.
I know the yakkers hand up when the subway train goes into the tunnel and don't resume until they get out of it. But ne'er the less these rooms are shielded. Even your Super Phone wouldn't work there.
Special measures had to be taken to make the phone work in the tunnel. Basically put a cell in the tunnel itself. I've had mine go off and work just fine inside an elevator in a town (~40,000) in Nebraska. Hong Kong has the advantage (for purposes of cell phone coverage) of a very dense population in a relatively small area. Most places in the US have much lower population densities, but cell tower coverage and signal strength only depend on distance from the tower (and shielding by terrain or buildings of course). Since there is also a limitation on how much traffic any one cell can handle, in Hong Kong the cells are going to be more closely spaced to limit the number of users in each cell. This result in higher signal strength. In most of the US, we have a lot more "elbow room", with lower density of users, and thus the cells are larger. This results in a lower signal strength and more fringe areas.