Using molecular dynamics simulation, we show that the vibrational relaxation lifetime of a diatomic in a two-dimensional supercritical rare-gas fluid exhibits the same unexpected plateau behavior as was observed experimentally for W(CO)(6) in supercritical CO2 by Fayer and co-workers, and we link this behavior to average local solvent density enhancements arising from the solvent＇s near-critical density fluctuations.