who is the home team in a bowl game and why?

With the exception of the Bowl Championship Series Games (Rose Bowl, Orange Bowl, Fiesta Bowl, Sugar Bowl, National Championship, which are based on BCS Rankings, the home teams for the Bowl games are generally selected by the Bowl Host/Sponsor. Many Bowls have pick the teams who play based on Conference and finsih, i.e. the Holiday Bowl: Pac Ten #2 vs Big Twelve #3. The home team rotates yearly, Pac Ten #2, Cal, is home.

For the BCS Championship -- It is the team that was #1 in the BCS rankings that gets to wear their home jerseys

For the Super Bowl -- The designated "home team" alternates between the NFC team in odd-numbered years (the Philadelphia Eagles in 2005), and the AFC team in even-numbered years (the Pittsburgh Steelers in 2006). The home team is given the choice of either wearing their colored jerseys or their white ones; this started with Super Bowl XIII. Prior to that, the home team always wore the dark jerseys. The Dallas Cowboys wore their rarely used blue uniform tops in Super Bowl V, and lost to the then-Baltimore Colts, which has led to the widely held belief that the Cowboys do not play well in their blue shirts. While most home teams in the Super Bowl choose to wear their colored jerseys, only the Cowboys in XIII and XXVII, the Washington Redskins in XVII, and the Pittsburgh Steelers in Super Bowl XL have worn white as the home team.

If by bowl, you mean the sport of bowling it's be which ever team is sponsored by that house, if bowl as in rose bowl or super bowl...I have no idea