Only this morning, the papers were announcing the completely unsurprising puff of black smoke indicating that the first round of balloting in the Sistene Chapel failed to produce a 2/3 majority. Typically, dozens of rounds of voting are required. It takes some time to arrive at a consensus, after all. Plus, some were concerned that the new rules John Paul instituted would give the hardliners an incentive to draw out the process (after 30 rounds of voting, a simple majority can decide).
In many ways, this is not an astonishing result, even if the haste with which it was accomplished is unusual. Ratzinger was appointed to lead the Congregation for the Doctrine of the Faith back in 1981, and is about as close as you can get to a doctrinal duplicate of John Paul II. There's another reason, too. The man is old, already 78. After a long, eventful Papacy, perhaps the College of Cardinals is wary of too-hastily setting the direction of the Church for another 30 years. So we may expect a handful of years with no major changes in direction. Benedict XVI will be seen as an interim Pope.
The rapidity of today's events only means that a large majority of the Cardinals felt the same way.