In simpler terms: The main difference between DTube and Youtube is that DTube is decentralized. 

Youtube runs on a system owned and operated by an organization (Google) giving them full access and authority over those who had signed.in and used Youtube before. The control is owned by one large organization. If Google wants to, they can suspend/terminate any account just because they can and have the full power and authority to do so.

Decentralized Apps (DApps) like DTube however are free from any control and interference from any single authority. Every user using the app is somewhat considered the owner of the app and/or share some stake over it. That is why DApps cannot suspend nor terminate any account because they have no full power and authority to do so and is also the reason why there are NO ADVERTISEMENTS on DApps. Since everybody somewhat owns the app, the advertisers have to pay everybody first before they can start advertising.

It is worth to note that DTube is built on top of the Steem Blockchain and must also adhere to ALL its rules and mechanisms. Which is why there is another huge difference on how content creators are being payed on this two platforms. At the moment, DTube only allows content creators up to 7 days to accumulate payout rewards in terms of an upvote unlike Youtube's eternity. Any content (video) after 7 days on DTube are no longer rewarded which honestly is discouraging and somewhat unfair to some vloggers especially people who only have a small following.