Helping verbs seem to be somewhat exclusive to english...at least as far as i can see. Maybe this is the situation here? Maybe not.
As a native english speaker i do see "is" as necessary...like mentioning the existence of a thing is required to inquire about it. My swahili isnt great...neither is my english. Maybe "is" isnt a "helping verb" in this case and thats why we really want it to be there. I dont know. Maybe im off base.