Manipulating the scales on graphs is one of the oldest tricks in the book. It's one of the many deceitful practices that Edward Tufte talks about in The Visual Display of Quantitative Information. In fact, in the chapter on "Graphical Integrity", he writes: "For many people the first word that comes to mind when they think about statistical charts is 'lie'."
If I were interested in investing in Twitter stock, I wouldn't be nearly as concerned with the growth of their user population as I'd be in the growth of their bottom line (profits). Oh, sorry, there are no profits.[1] As they say, "you can't make up losses on volume".