Not really. If you cut the sigmoid in half they do look similar, but that doesn't mean that they're the same function. They behave differently (the Sigmoid has an inflection point, which is a Big Deal), but more importantly, they represent different types of relationships. The final graph shows population growth or network effects, both of which have the potential to be unbounded[1]. The sigmoid has a definite carrying capacity. In fact, knowing if your chart is really the last one or the first half of a sigmoid is very useful, because that tells you whether you need to plan for an inflection point.

[1] This depends on what the x-axis represents. If you're plotting against time, you'll always be bounded due to finite resources. If you're plotting against resources or network size, value and even marginal value can be unbounded.