That list is a bit odd -- as I notice 3 companies on there that I don't really think have a "DCS" platform. Automation World is a very trusted publication/media source, so they must have some reasoning behind that list.
That said, I would not get to caught up on terminology. The lines have blurred between PLC's, PAC's and DCS's in the past decade or so. Each has taken on features and characteristics of the other. So, as Mary said, maybe just focus on what your application is and fit the right vendor platform for the job. Determine your inputs/outputs by location, networking infrastructure, how much control will be centralized vs. distributed, and what your needs are with regard to HMI.
I hope this helps.