0 BB, 0 K Complete Games

I've focused a lot on the offensive side of things so far, so let's look at the men on the hill. Since 1957, there have been 61 complete games in which a pitcher has neither walked nor struck out a single batter. Here's the most recent five; the dates link to the box score and play-by-play of the game:

1. Joel Piniero, 5/1/2006, 9.0 IP, 9 H, 2 R, 2 ER, 1 HR, 106 pitches, 77 strikes
2. Pedro Astacio, 4/24/1994, 9.0 IP, 7 H, 1 R, 1 ER, 0 HR, 108 pitches, 67 strikes
3. Tom Glavine, 6/15/1993, 9.0 IP, 6 H, 1 R, 1 ER, 1 HR, 79 pitches, 53 strikes
   
4. Bill Wegman, 7/11/1992, 9.0 IP, 13 H, 1 R, 1 ER, 0 HR, 134 pitches, 84 strikes
5. Bill Gullickson, 5/26/1992, 9.0 IP, 6 H, 1 R, 1 ER, 0 HR, 84 pitches, 55 strikes

The entire list can be found by clicking here. It's interesting that they happened at least once a year from 1957-1994, except for 1960, 1970, and 1984 and then there was a twelve year break between 1994 and 2006. Have bullpens specialized that much more since thirteen years ago?