By hinging the tail at an angle, there must be enough thrust on the turbine to actually lift up the tail a small amount (because of gravity). If you notice when turbines are fully furled their tails point up at a funny angle, that's because they are pushing pushed up by the moment of the turbine and held up by the wind which is going by the tail vane.
The math can be difficult and from what I hear it doesn't give very predictable results for homebrew turbines sometimes. The variables are pretty hard to control from turbine to turbine though, even given the same design.
I would definitely say that the main reason for having a furling setup this way is simplicity. Once it works, it doesn't use any additional power or electrical control system, it keeps the turbine safe and is pretty cost effective.
However, there are turbines that use a sort of jack arm to furl. Many air compressing wind turbines used by the amish do just that. You can see a few of them on this site: http://airliftech.com/
Once there is enough pressure built up it trips a valve which pressurizes the arm and furls the mill. Pretty cool really.
