Your statement is partially true...while there are many NPC's that do not have last names, there are many that do as well.

Examples:

Abylgo Hamylgo and Fineco Romanecco are both Lalafells that are within the Gladiators Guild in Uldah.

Bango Zango is a Lalafell in Limsa that is a major NPC for Crafting Leves.

Nonco Menanco is a Lalafell in/around the Adventurers Guild in Gridania

Roosting Crow is a Roegadyn, also Rubh Epocan and Daca Jinjahl are Miqo'tes... all three reside in Limsa.


So yes, some NPCs in the game do carry last names just like our characters.