It's because you haven't specified a result_type in the parameters of your mysql_fetch_array, it therefore defaults to MYSQL_BOTH. so your array would look like
Array (
[0] => 001 [id] => 001
[1] => Fred [name] => Fred
[2] => 100 [hours] => 100
[3] => 7 [MAX(pipereps)] => 7)
Whereas if you had used mysql_fetch_row or your mysql_fetch-array statement was like this
$rw = @mysql_fetch_array($maxuser, MYSQL_Num)or die()
then your array would look like
Array (
[0] => 001
[1] => Fred
[2] => 100
[3] => 7