The article isn't really covering the modern pinball scene. While Stern is definitely the major manufacturer in play, Jersey Jack is growing and there are several more boutique manufacturers including:

Multimorphic - Offers the P3 pinball system integrating a full LCD panel with motion tracking into the playfield (as opposed to the backbox like JJ.) They also offer the P-ROC which allows replacing the CPU (a 6809/ASIC combo!) with a Spartan3 system allowing you to reprogram the rules on most 90's+ games.

Spooky Pinball - Ben Heck designed the America's Most Haunted machine, an "unlicensed" theme that is quite fun to play. I believe the first run was for 150 machines, with the next title to be announced in the near future.

Heighway Pinball - Manufacturer out of England with one title in production (Full Throttle, a motorbike theme) and are working on a licensed Alien themed pin.

There are a couple others including current and former game designers working on their own or with one of the manufacturers. This also says nothing of the pinball modding community, custom one-off games, etc.

EDIT: Completely forgot Planetary Pinball who is remaking late 90's pinball machines with modern electronics. First machine is Medieval Madness and is shipping now.