Instagram last night announced that the social network has has reached 400 million global active users, a jump of 100 million this year, posting 80 million photos and videos a day. This comes quickly after we heard just two weeks ago that WhatsApp has now reached 900 million active users globally of the messaging app.

The two sister companies certainly seem to be getting something right, with pretty staggering growth numbers. They are very much pulling away from the likes of Twitter and LinkedIn. Remember, Twitter has has only 316 million active users, a total which the company has hovered around for the last year. And Linkedin is at just 380 million registered members (it doesn't count its users the same way as the others - the active users would be far lower).

So where are Instagram and WhatsApp getting it right?

Instagram has announced that it added 100 million users this year. The biggest growth has come from Brazil, Indonesia and Japan. It has introduced new functions like landscape and portrait sized photos. forwarding photos to friends, and direct messaging, yet all the while it has remained very simple to use, something that is clearly resonating with new users, and I would say is something neither Twitter not LinkedIn can boast.

WhatsApp's utility and simplicity continues to be its main asset. This year it released web.whatsapp.com to allow its users to flip from app to laptop seamlessly.

Over the coming weeks and months it will be interesting to see how Twitter and LinkedIn's own numbers grow, and whether we see any radical changes to their platforms to channel the simplicity which is clearly so important for growth in this space.