Cancer stem cells--Their existence and their implications

Are there tumor stem cells for all tumors? This is a great question. The short answer is so far no one knows. They are identified in blood, breast, brain, colon, and head & neck (unpublished) cancers so far, and i believe there will be more. No, the presence of tumor stem cell does not refer that cancer arises from stem cells, however, tumor stem cells are thought to be the driving force for the tumor renewal. So, without these cells, the tumor should exhaust itself. So far, in tissues where tumor stem cells are identified, the tumors are always heterogeneous. Heterogeneous based on the markers used to sort the tumor stem cells. Tumor stem cells are also always the minor population of the tumor, but when put into mice they can generate various different cells with different marker profiles. The interesting question is why are tumors made of heterogeneous cells, do they need various cells to survive, for support? If tumor stem cells are the driving force for tumors, why doesn't tumors just consist of only tumor stem cells?

Couldn't the explanation of heterogeneity simply be that the cells are different? I know that the cancer stem cell field likes to use heterogeneity as a line of evidence for their hypothesis, but to an outsider the fact that cells within a tumor are different doesn't seem that interesting and perhaps not that surprising. One could hypothesize that the cells are different due to changes caused by genomic instability and their differences are not significant at all. Why does the fact that the cells are different mean that there are cancer stem cells?