The fact that they're 1-2 in the app store probably has more to do with the Instagram sale than any pent up demand for video sharing. It makes sense that they're both raising money--they've got to fund their massive UA campaigns.
The reason they're at the top of the app store is because they built a great product that millions of people love. Video is a core technology on mobile devices and until now it's been really hard to record and post a video to Facebook/Twitter.
That wasn't meant as a disparagement on their products--but app quality and app store ranking often have very little to do with each other. Unless by "until now" you don't mean "until Instagram sold for $1 billion", I don't think the technology has radically shifted in the last couple of weeks.
