why isn't the head umpire called the umperor?

Tonight's home plate umpire for the Astros' contest against the Detroit Tigers is scheduled to be CB Bucknor. Bucknor has called 3 of Craig Biggio's 277 HBPs, and through the end of last season, he had declared 188 total batters "plunked" in his career. Bucknor calls HBPs at a rate of 0.73 per game, which is slightly higher than the league-wide average for the span of his career, which is 0.70. Bucknor ranks 32nd in average plunks called per game in that span, and 36th in total hit batters awarded first base. Of the 188 plunks he's called, 105 have been the visiting team getting hit, while only 83 were the home team. From 1996-2005 (the years Bucknor has umpired in the majors), only 5 umpires have had a greater discrepancy in plunks called in the direction of the visitors. Bucknor has also called 14 total HBPs for Houston batters (in 25 games), but only 2 for Detroit (in 16 games).

During the span of Craig Biggio's career (through '05), Tim Tschida leads all umpires with 395 plunks called, but in terms of plunks per game, Bill Welke leads the way (among umpires with more than 50 games behind the plate) with 0.90 per game. Tim Tschida, Tim Welke, Gary Cederstrom and Chuck Merriweather all tied for calling the most plunks for the Tigers with 24 each, while Dana Demuth has called the most for the Astros with 33. Bill Welke called the most in a single year (since 1988) with 43 in 2001.
(For Biggio's HBPs by umpire, look here, then add 2 for Bruce Dreckman, 1 each for Greg Gibson, Jim Reynolds, Lance Barksdale, Ted Barret, Bob Davidson and Brian Gorman)