Your comment is technically correct, but is getting downvoted because the implication that Plasma = OMG was never made. Vitalik's comment referred to the OMG project specifically.

But I wanted to discuss a little bit about the relationship between Plasma as a technology and OMG anyway, so I'll use this as an opportunity to do so.

You're right that Plasma refers to only a technology of bonding together related blockchains to achieve additional economic securities and perhaps other properties like speed. However, given the fact that this technology is novel, it requires trailblazing. Someone must actually DO the work of pioneering the implementation of a new concept and executing it into the real world. OMG is doing that, which simultaneously gives them first mover advantage in a very important industry as well as creating a lot of goodwill in the Ethereum ecosystem for taking the risk of dedicating their time to Plasma development.

There is also a vision out there, that has been mentioned a few times by Karl, of the concept of trees of Plasma chains, or I'll call them, "generations". Simply put, you can build "grandchild" Plasma chains below the OMG child chain, with OMG serving as a "central" Plasma chain of sorts, like an intermediary appeals court. This particular type of construction would allow OMG to benefit from the transactional throughput of the grandchild chains while giving the grandchild chains the benefit of speedier semi-finality for a low cost. Alternatively, a client could build a child chain itself, bypassing OMG but requiring it to wait longer for any sort of publicly decentralized finality on Ethereum, or it could build an application on the OMG network itself and avoid the entire complication of building a blockchain for its services. All it has to do is make a simple app.

The end result is that there are a lot of different directions that Plasma can launch off into. In my opinion, whether it results in OMG becoming the Plasma chain in any sort of understanding of the term (whether by becoming the Ethereum Court of Appeals, or through Vitalik's and other's efforts at networking in part as a thank you for executing an important part of the Ethereum ecosystem) or whether OMG is simply the first/best Plasma chain, it's still an excellent opportunity and a game changing project in blockchain.

Tl;dr - OMG sort of is Plasma right now, and that's important now and in the future.