I'm sorry. I really am. I know this isn't Reddit. But...
HAHAHAHAHAHHAHAHAHAHAHAHAHAHAHAHHAHAHAHAHAHAHAHHAHAHA
Yes. Yes, on average, a given tweet reaches ONE HUNDRED PEOPLE. Do any of you folks even listen to yourself? Even if you change that to "users" instead of "people," since so many twitter accounts are robots - even then, 100 users on average for every tweet is ABSURD.
> the polling that twitter applications do even when there are no new tweets
Polling with no new tweets is far easier to optimize than polling when there are tweets. So just discount this almost entirely in your roughshod analysis.
> spam filtering
Have you been on twitter? We all get spam and see fake accounts trying to get at us regularly. Try mentioning you're on a diet on twitter and see how many followers you rack up. If they're filtering spam, they're not filtering it well, so I hope they aren't burning too much cash on it.
> API servers
API servers are frontends that use dramatically fewer resources than the work the backends have to do. If Twitter's frontends are costing them much money, again, they're wasting money.