This paper addresses several key issues regarding the statistics of Langmuir wave fields E in planetary foreshocks by presenting (1) a detailed theory for the electric field strength probability distributions averaged over Earth's foreshock and (2) the first analyses of the distributions observed in the outer planets. First, existing theory is extended and generalized, describing in detail how lognormal distributions of P(log E) for a specific location can be aggregated over foreshock location to give power law distributions $overline{P}$(log E). The extended theory is in good agreement with the observations of power law distributions $overline{P}$(log E) for Earth's foreshock, and implies that stochastic growth theory (SGT) is likely to be relevant. The statistics of the Langmuir wave fields of the outer planets Saturn, Uranus, and Neptune are then analyzed and compared. The characteristics of the observed distributions $overline{P}$(logE) agree qualitatively with each other and Earth, and these distributions collapse onto a single curve when scaled on the assumption that the ratio of the wave energy density to thermal plasma energy density is constant with heliocentric distance. The extended theory developed for Earth is also found to agree well with the scaled $overline{P}$(log E) distributions for each outer planet. The evidence is thus that the physics of electrons and Langmuir waves in all planetary foreshocks is essentially identical and that the distributions $overline{P}$(log E) are consistent with SGT.