Are there many winners with this model to name. Maybe NGINX, MongoDB?
Whenever you see "open core," you should read it as "VCs said we need to do this to keep them happy."
VCs love the idea of how you can give part of something away for free then lock people in to auto-renewing subscription contracts for the whole banana (with fees increasing 7% to 17% every year for ongoing "maintenance"). Many VCs still actively recoil at the thought of giving away everything for free then just hoping the best will happen.
Nginx is a weird example because I'm not sure how well they are doing or who would buy "nginx pro" instead of haproxy+nginx or haproxy+varnish+nginx some other combination of already existing stuff.
MongoDB is an interesting example because they went with the "provide open software, but with really serious, game-stopping flaws, then force people to pay for support because nothing works" route. That's almost literally bait-and-switch (bait-and-support?). But, that hasn't ended up so well for them. From a recent WSJ article: Fidelity has cut its valuation of MongoDB in eight of the nine quarters since Fidelity made its investment in December 2013, valuing the shares 58% below what it paid.
Do you have a link to the MongoDB WSJ article? They are pretty terrible, even with a support contract bugs have a way of not being resolved or addressed.
I think this is a reasonable model. It's not easy to build / sustain complex software and while it works for a lot of projects, maybe majority of projects get neglected or depends on a few dedicated contributors. Who often burns out etc.
It also provides some confidence to users (at least to me). I know the project is open source. If the backing company goes evil, a fork can always emerge (iojs comes to mind). And I also know that some people are making money over this software and they will keep it alive / work on it as long as it sustains the business.