I don't get this. Why do you, apparently, think you should be the one defining what ADD and ADHD mean, rather than doctors defining them? That's so weird. What if someone tried to tell you that "cancer" is used to define way too many diseases? I'm certain you'd think they were being ridiculous.
The distinction is that ADD/ADHD has vague symptoms that can belong to a crap-load of different diseases/neuroses, or just be related to character, or be a result of bad parenting/behaviour (consider having too much freedom, not enough control).
Cancer is pretty definitive to diagnose.
You either have a cancer, or you don't.
It's a physical thing you can find in the body, that physically effects the body, and you can identify it in the blood, or urine, or through CT/MRI scans, or even see it on a persons body.
You can't do any of that for ADD/ADHD. It is literally a case of a doctors opinion based on a persons behaviour.
And behaviours, by the way, can also be put on on purpose.