The book sold many copies. Without knowing the author, I can only suggest that if he didn't mean to preach a "Health and Wealth" gospel, people were misinterpreting him.
Why do I say Jabez was a whiner? Listen to how the verses read in the New International Readers Version:
Jabez was more respected than his brothers. His mother had named him Jabez. She had said, "I was in a lot of pain when he was born." Jabez cried out to the God of Israel. He said, "I wish you would bless me. I wish you would give me more territory. Let your powerful hand be with me. Keep me from harm. Then I won't have any pain." God gave him what he asked for.
Why people think that because Jabez did this, it will work for me, I don't know. Somehow I must have missed the prayer that Jesus prayed to do the same.
I do remember the story of the widow who complained to the judge and here request was granted. I remember more, the commands to feed the poor, care for the widow, give water to the thirsty and cloth the naked.
I may be way off base but... This is a discussion that still pops up in our house from time to time but I don't think Jabez's prayer is as favored as the author would like it to be.