Sure Dapps might be an interesting concept but let's not pretend it is free from manipulation. Miners are the gatekeepers to the system.
F2Pool is one of the biggest pools in Ethereum. It was alleged that they manipulated the Status ICO:
https://themerkle.com/f2pool-allegedly-prevented-users-from-...
They controlled 26.6% of the total Ethereum hashing power.
So, lets say this twitter clone - Peepeth takes off. And then there is someone who wants to post some stuff against F2pool. What is stopping F2pool from manipulating the feed? You might say other miners controlling 75% of the hashrate will pick it up. Sure, you might be correct. But what if the post shits on every other mining pool out there? What happens then? What if the post is time sensitive?
Decentralized apps can only go so far considering there has to be a record for the system to work. And if record keepers manipulate the system it will fail. The question becomes then:
Quis custodiet ipsos custodes?