That does seem to be the new business plan: 1) develop service, 2) let others figure out a monetization strategy 3) do it yourself and change your TOS 4) repeat from step 2
That's hardly fair. Paid tweets are a blindingly obvious method for generating revenue - they're just Twitter's version of advertorials. The hard part is, as they say here, trying to have paid tweets that do not ruin the user experience.
Given how many webpages look these days, with more ads than content, they can't really be blamed for being concerned about third-party advertising ruining the service.
A more delicate way to handle the situation would have been to acquire one of the ad networks or at least launch their own service to compete with the others instead of making such an aggressive move. Facebook has been working to take marketshare from their platform's ad networks with their own credits and offers system, but it doing it in a slow, deliberate way that is not traumatizing their platform ecosystem.
