Don't post when one is tired. Words get left out.
As Wade stated, injectors wear out, but they are not in the same category as spark plugs and need periodic routine replacment at a fixed miles or hours point.
The BS Line I've heard is from diesel shops that are looking only to sell you a set injectors. If they put in a set of larger injectors, the unsuspecting person will notice a nice feeling in the butt-o-meter and mostly be happy with something they didn't need.
Now, if your looking for an excuse to upgrade, that is entirely a different story.