Earlier works on discharges sustained by electromagnetic surface waves in absence of a magnetic field have revealed the central role played by the power balance per electron. This balance relation stated that, provided energy transport is negligible, the power theta(L) lost by the electron an the average in collisions with heavy particles is exactly compensated under steady-state conditions by the power theta(A) taken by the electron on the average from the high frequency (hf) field, their common value being the parameter theta. Then, because theta(L) is to a first approximation the same in all hf discharges under given discharge conditions and power density, a simple discharge model valid for all hf plasmas was used. The present article is an extension of this approach to hf magnetized plasmas, using surface-wave plasma columns placed in an axially directed static magnetic field as a means of investigation. We observe that theta decreases monotonously when increasing the magnetic field intensity B-o, showing no extremum at or close to the electron cyclotron resonance frequency match over the gas pressure range (5-100 mTorr) investigated. We show that theta is controlled either by classical ambipolar diffusion or anomalous diffusion, the actual diffusion regime depending on whether the novel parameter B(o)p (p is gas pressure) is small or large. Our measured theta values are further used to estimate the average electron density in helicon sources given the power density, showing fair agreement with the reported values.