Stephen, perhaps you may want to start a thread under comparative religion for your questions. Your presence here is an opportunity to learn more about Islam. If you have legitimate concerns and questions about what Islam teaches then you are welcome to bring those forward if (and I believe you can) you can present them in a respectful manner.
Regarding the reason why we were created to worship God, I think it answers a basic human question for his existence. My take on the verse you mentioned is that we were created in a manner that we have the choice to worship God, or not. We were not created as robots like the angels to always do the will of God, but rather every day we Muslims choose between submitting to His will, or not. I have made the decision to follow Prophet Muhammad (saaws) in what I believe about God and the unseen and in how I live my life, including how I worship God. I am not one to even approach understanding God's motives for creating humans to worship Him; however, I choose this Path and I hope in the promised reward for those who do.