The tight ends are still very useful. They are great blockers on the running downs, impact players on special teams. However, if you have a player of Antonio Gates caliber, you can easily have a catching threat as well. So they are useful as well.
Rob is hardly the final word for whether a tight end is useful or not. Jason Witten, Vernon Davis, Antonio Gates, Dallas Clark and many more have proven the usefulness of a tight end. I don't even know why or how this question was even asked.
A big-time WR and a top tier TE are the best friends a QB has. TE are more important now than ever; they used to just be blockers that could catch better than an OL. Now they are impact players; especially if a team has a young QB.