Ah, I see now. This may help
explain-http://microsite.omniture.com/t2/help/en_US/mchannel/index.html#First_and_Last_Touch"Every
success event instance will have exactly one First Touch channel and
exactly one Last Touch channel. This means that if you add up a given
metric column for any success event, it will always exactly equal the
total for the same time period. Non-success event metrics, such as
visits and visitors, will not match up 1 to 1, as multiple channels can
fire in the same visit."...