Well then...there goes my theory! Like others said...when Zimm comes back and Morse gets in you will see the offense pick up significantly. Other guys (LaRoche/Werth) will start seeing better pitches because they won't want to pitch to Zimm, Morse, or Harper.
From June 1 onward, RZ and Morse combined for 116 RBI last year. Given that last year's team was fairly comparable to this year's team in terms of OBP, I'd say that's a good "fuzzy math" starting point.