This letter examines the impact of oscillator phase noise on sub-terahertz OFDM transceiver architectures, with a focus on the comparison between homodyne and heterodyne designs. Using a Hexa-X compliant phase noise model, we analytically show that heterodyne architectures reduce the total accumulated phase noise variance by distributing frequency translation across lower-frequency oscillators under realistic phase-noise scaling laws, thereby shifting the dominant impairment from inter-carrier interference to common phase error. OFDM simulations at 70 GHz and 140 GHz demonstrate that while homodyne architectures remain competitive at mmWave frequencies, heterodyne designs provide improved robustness to phase noise at higher sub-THz carriers. These results highlight transceiver architecture as a key design lever for relaxing oscillator and phase-locked loop constraints in future sub-THz wireless systems.