User blog comment:FairyRaven/Fairy Tail Chapter 325: Unity, Review and Commentary/@comment-71.146.139.183-20130401051141/@comment-7418318-20130401073143

Sama is simply a sign for great respect (most of the time anyway). Lord and Lady are titles bestowed on nobility. While every Lord and Lady would be -sama in japanese, the reverse is not the case.

In japanese calling a respected and famous scholar, actor or artist -sama is nothing out of the ordinary, but calling such people Lord or Lady would be odd.

It can even be used sarcastically to mock someone, like Ultear did when talking to Hades about "Jellal-sama" and him having been so easy to dupe.