Whether it applies here or not, Fred Saberhagen, in his novel "An Old Friend Of The Family" has Dracula using a shaving "mirror" consisting of a video camera and a screen large enough to reproduce a life sized image of himself. I know, Mr Saberhagen isn't Joss, and Dracula isn't Angel, but a similar technique might be used by Angel, and Spike's hair style doesn't require a mirror, just comb it straight back and paste it down.
And while I agree, we are probably overthinking such a minor point, certain people here would be quick to point out that overthinking is one of my favorite pastimes.