The concentration of live microorganisms present in yoghurt is unknown but will tend to be relatively low and will depend on the freshness of the yoghurt and the conditions in which it has been stored. After opening, the microbial concentration can become depleted. Compare this with the high and guaranteed concentration of probiotics in the ProBiotic LIVE products.
The actual strains of microorganisms contained within live yoghurts will tend to be chosen for taste and textural properties rather than a probiotic benefit. The micro-organisms contained within the yoghurt may not produce any probiotic benefit.