This is very true. I find the saddest thing is that most all martial arts have some value to them and many are similiar in both approach and technique. There are only so many ways the human body moves, and many of these methods are the same.
For example:
Karate Reverse Punch- Comes from the back hand, held at the ribcage or at the head (depending on the target) the fist turns over as the punch is rotated forward, feet, legs, hips, torso all work together for impact power.
Boxing Cross- Same as above.
Pai Lum Side Thrust Kick- From front or side stance, back leg steps, front leg chambers, kick shoots out kicking with the heel and the hips turned over, re-chamber, back to stance.
Taekwondo- Same as above. (According to one lesser member here, Taekwondo has no value.
)
Muay Thai Plum- After entering your opponent's space, hands shoot behind the neck for head control. Forearm press down across opponents collarbones, head control is key. Where the head goes, the body follows.
Shuai Jiao Clinch- Same as above. (This is merely a part of Shuai Jiao but the point is taken.)
Now ask yourself this, does it matter where something came from. I'm sure all of have worked out with a fellow martial artist that taught us something and we learned from it. Does that stagnate what you know because it came from another source??
In the end we are all humans with two arms and two legs, nothing more.