From the Wikipedia page for the vermiform appendix:
This proposal is based on a new understanding of how the immune system supports the growth of beneficial intestinal bacteria, in combination with many well-known features of the appendix, including its architecture, its location just below the normal one-way flow of food and germs in the large intestine, and its association with copious amounts of immune tissue. Research...showed that individuals without an appendix were four times more likely to have a recurrence of Clostridium difficile.
This quote seems to be implying that the appendix can act as a breeding ground for certain gut flora that are slightly less common (like C. difficile) and not as ubiquitous as E. coli or Enterobacter sp. The appendix could be seen as an ideal spot for this growth of microbial populations in the gut.
Given that, to a first approximation, anatomically, the appendix and a common diverticulum of the colon are both outcroppings of the large intestine: to what extent would a diverticulum also be able to support less common or more diverse flora, and how likely is this to be due to a difference in extracellular environment (pH, ion concentration) and how likely is it simply due to shape?