[sametmax]

Also:

- whatsapp doesn't have to allow browsing the entire history of their billions of messages;

- whatsapp doesn't have tags. A message can go not only to 1000000 users, but also to so many apps requesting updates for one tag.

- Twitter allows advanced search, where you can browse, in real time (or down to the entire history), a complex combination of people, tags and free text. With settings such as choosing the lang or the date.

- Whatsapp has a list of messages. But Twitter has a graph : message can be RT again and again, answered to and liked.

- all those features have some impact or the other on the way the tweets are displayed to the user.

- Twitter's API is much more used than Whatsapp's.

[jraedisch]

WhatsApp also does not need ad related analytics.

[monocasa]

That's a big leap. They don't have to actually show ads for that analytics data to be extremely valuable.