My own take is not that prayer is useless, but they are two sides of the same coin. Prayer is intent, usually for others. Meditation is the response for one's self.
Personally, I have found the most simple prayers to be the most powerful: "God, help me!" in honest despiration is one of THE most powerful prayers there is. Another is a simple "god bless so-n-so", and leave it at that. This is a good one when there is strife, or resentment, or anger with someone - praying for them allowing "god's" will to be done instead of our will <murder or severe hurt comes to mind>, has had some amazing results that I've experienced and have heard of experiences of others.
As the article suggests, Prayer differentiates, separates, individualizes. Meditation unifies and opens us up for the answers we need even when we don't know how to form the questions.
I personally believe that we are "spiritual beings having a human experience".