Black tarry stools can also indicate upper (or sometimes lower) bleeding. Their medical name is "melena" (you might like to look this up on a medical website).
If your stools are indeed "melena" then I would urge a colonoscopy and endoscopy to determine the bleeding source.
Morecambe
At this point in time, there's a fairly decent correlation between the presence of gastric H. pylori and GI issues. there is also a good correlation between at least one form of H. pylori and other systemic problems, so it's felt that treatment in necessary. Within the medical community I believe treatment using antibiotics teamed with acid-suppression meds has been shown to be the best method of knocking out a high percentage of H. pylori infections. Yet even with teaming 2 potent antibiotics with PPIs it's not always effective. I haven't read of any other methods of treatment that proved to be effective, so antibiotic therapy has become the 'standard.'
I'm not sure what you're asking in the second part of your question.