That is how it is spelt Pierre. Like Coward and Cowherd, words get bastardised. While shephard is how it is spelt usually, shepard without the h is a throwback to the days before spelling had a common standard. People don't go around changing their names because their friends said "you're spelling it wrong".
In other words, his namesake, the Opfor char spells his name "Shepard".
[edit] What the *()$*()@$%W%(!!???? I could have sworn my game spelt it without the h, but I just checked the model viewer and the model is called "shephard".
I could have sworn, because I remember making a similar point before...???