In the 1990s sometime, when Pope JP II was seen to be less vigorous, even in decline according to some, I saw several talking heads speculate that his successor would be a caretaker, a little older, to ensure (so it was thought) a shorter reign, to give the church some breathing space. Ratzinger is gettin' up there in years.
However, it was recently pointed out (again by a talking head) that the strategy may not hold, because of the advances in geriatric health care. IOW, Benedict XVI may be around twenty more years.
Benedict XV:
http://www.catholic-forum.com/saints/pope0258.htm
One thing to realize is that Ratzinger has worn his spiritual and theological heart on his sleeve for decades -- he is an incredibly open person. He has done three, count 'em, three book-length interviews with journalists where he responded openly to every possible question about his outlook and beliefs. He's written his memoirs. And that sermon the other day was another example of the same -- no campaign oratory, but a cry from the heart.
The cardinals had to know exactly what they were getting.
Besides, the last time they picked an old guy to just sit quietly on things for a few years they got John XXIII. Surely that would make anyone skeptical of a "caretaker" option.