Well, for a headphone amp, it is. The thing about headphone amps is that you can make them like integrated amps, with tape outs, source switches, 464-band mega super mondo EQ, but most aren't like that. Most headphone amps are just the headphone amplifier with a volume control, so you don't need a preamp. If you were to leave off the volume control (one of the amps I built a while ago had a separate volume control; the end-user ended up just using it without the volume control on the output of his preamp), you've got a "headphone power amp".
Is this what you meant?