It's not the same exact market but its essentially the same business model - build a community around an open source system and then upsell enterprise customers on support, consulting & services.
Big difference is in fact apparent right there in your original post: There are two (actually three plus more) vendors backing hadoop, an amorphous community based around an Apache foundation project that no commercial entity controls. This means the Hadoop ecosystem, while generating plenty of value, is not one that can be captured by a particular firm. Plus, the operational database market is ultimately far larger than the Hadoop ecosystem, and so taking a reasonable bite out of it means a materially different market. Finally, it's not just about control of the market, but the software license. Hadoop vendors have little defense of an Apache licensed stack, and face massive threats from new cloud offerings.
Good points. For what its worth there are other successful MongoDB hosting providers - mLab (originally MongoLab), compose (originally MongoHQ), and ObjectRocket - so they (MongoDB, Inc) don't have complete control over the ecosystem, despite the AGPL licensing. Well, they do have the market for support cornered, but long term the margins on that are much lower than DBaaS.
I think a larger issue for MongoDB (& Hortonworks/Cloudera/MapR) is Amazon/GCS/Microsoft hosted services that obsolete them for many use cases. MS already has Azure DocumentDB that supports ACID transactions and has a MongoDB compatible API.
