Voldemort's name

[tobyreiner]

No: HPFGUIDX 81941

Ok, I'm new to the forum so if this has been asked long ago, please 
forgive me. 

I've never understood why Voldemort's enemies call him "Lord 
Voldemort", when they're not calling him "He Who Must Not Be Named". 
Lord Voldemort isn't his real name, and it's bizarre that his claims 
to lordship should be so readily accepted by Dumbledore et al. 
Indeed, Dumbledore does call him Tom when they duel at the end of 
OotP, but always as Voldemort when referring to him to others. It's 
like Yoda and Obi-Wan Kenobi talking about the "Emperor" in Star 
Wars, even though they never accepted Palpatine as an Emperor of 
anything. 

Why? Just for convenience?