Great book on carrying the message. This is the third book of David Platt's I have read. He certainly stresses the importance of taking the gospel to other nations. The great comission is still just as much a command for us as it was for the early disciples. However this book leaves you with the impression that if you don't quit your job and move overseas or relocate into an inner city environment that you are a poor example of a Christian. I would point out the following:
In the book of Acts Christianity first began spreading with the persecution following Stephen's death ACTS 8:1-2. The apostles however remained in Jerusalem. Paul then has his conversion and later begins his missionary journeys establishing churches through out the eastern Mediterranian.
While a number of converts to Christianity in the early history of the church left on missionary journeys a larger number remained in the cities they were converted in. Otherwise there would have been no local churches and no places for Paul to have sent the letters he wrote to. I think we can assume that not all of David Platt's congregation quit their jobs and moved to other countries otherwise he would not be pastoring a church in Birmingham.
I don't think the problem with Christianity in America is that we aren't sending enough missionairies overseas or to the inner city although those are both worthwhile missions that some people are called to. I suspect more of us though are called to service in our local church in some capacity. I think the question is what are we doing where God has put us to advance the kingdom of God. Are we living in a way that shows people what the gospel looks like?