In my experience, when a package like this is offerred it means a layoff is coming.  The company has decided, "We need to cut costs by X number of employees".  First they will "offer" a voluntary package which essentially gives "layoff terms" to anyone who wants it.  It is better than what you get if you just leave/retire normally, (ex. X months pay, X months medical benefits, etc).  So it can be a golden opportunity for those who were planning to leave/retire soon anyway.  The company will see how many people take the package voluntarily, then layoff the remaining number they need.
So although it means a layoff, it is generally a compasionate and generous way to benefit some and minimize the unwanted impact to others.
It happened to me.  I was going to retire anyway.  But by taking an "offer", I got all my normal retirement benefits plus a number of additional benefits.  The timing was perfect for me, and it saved somebody else from being layed off.