Let me first say, that I don't know John Piper's stance on every aspect of the Gospel. Indeed its quite possible that there are many aspects upon which we disagree. But I do believe his stance on the 'prosperity gospel' is logical and right.
It's tempting nowadays to seek an easy way out. Or to seek a pathway to the realization of all that God has for us that avoids pain or even poverty. There are some who even believe that if you believe in God 'hard enough' you won't have any hardships; if fact they believe that hardships are created by our lack of faith.
Piper's words speak directly to such people, as do the Words of Jesus: "In the world ye shall have tribulation: but be of good cheer ; I haveovercome the world" (John 16:33).