I've many times heard ministers talking about how when their son or daughter approaches them with a heart of gratitude and love and asks them for something, the child can get whatever he or she wants. This is used to illustrate how God provides us what we need when we ask Him in faith. The whole metaphor seems sort of flawed to me, though... if I had unlimited funds, would I give my son anything he asked me for? If I did, he would wind up spoiled and with no appreciation for any of it! And then again... does God give me anything at all that I ask for? Of course not. If I ask to be president of the moon, it's not likely to happen, at least not until someone LIVES on the moon. If I ask to be the owner of Microsoft... well, someone already owns Microsoft. And then there are the times when we feel we have made perfectly reasonable requests of God, and yet He does not seem to come through. What about those?
So what's my point? I don't exactly know. The Word specifically tells us that God will supply all of our needs... but I don't know that it says He will supply everything we want. I would never withhold food or clothing or shelter or love from my child, but I might withhold candy or a toy in certain situations. Maybe God, as our loving Father, works things out in a similar way. Maybe there's some sort of God-logic to when He answers "want" prayers. But I guess it doesn't hurt to ask, right? "You have not because you ask not" it says!
(I don't really want to be president of the moon, though.)