We report new results of investigations on the dewetting of confined thin polydimethylsiloxane (PDMS) liquid films (similar to 1 mu m thick) from a nonwettable solid surface, in various immiscible external bulk liquids (pure water and aqueous surfactant solutions). The dewetting parameters of these systems, contact angles (theta(E), theta(D)), and viscosity (eta(PDMS), eta(EL)) are such that they both should belong to the theoretical regime where dewetting is expected to proceed as at a solid-PDMS-air interface, leading to a dewetting velocity V scaling as eta(PDMS)(-1) (cf. to the subsection Position of the Problem and Previous Works). Our results do show some deviations from this, with velocities rather scaling as eta(PDMS)(-0.6) in surfactant solutions, while in pure water the eta(PDMS)(-1) dependence is found after normalizing velocities with the logarithmic prefactor. In addition, the dewetting velocity in surfactant solutions is found to be 2 orders of magnitude higher than in pure water. These results are discussed from a fundamental standpoint, based on the strong alteration of both the magnitude and molecular weight dependence of the logarithmic prefactor (cutoff length, rim structure) as well as the emergence of additional terms which depend on the nature of the external liquid.