When I planned and built my cab, playing the 90s DMD classics was of utmost importance to me (still is to a large degree). In a world dominated by LCD displays -- seriously, try to go 1 hour without looking at something that's LCD -- a real DMD was just more intriguing at the time, and I wanted at least that aspect of the cabinet to be authentic looking. They just look cooler to me... and different. Also, at the time there were performance implications with three LCD cab setups. A lot of people had problems getting it to work well. A side benefit of the PinDMD is that it took that additional load off the graphics controller(s).
Also, I think the color DMD stuff for real pins was still in its infancy at the time. Admittedly, I wasn't paying close attention to the trend, but it seemed like there was maybe 1-2 games that it worked with. Certainly didn't seem like a 'game changer' to me... more of a novelty for all the guys with real pins that were tired of the same ol' and itching to add something 'new' to their 20 year old machines. I still think it's mostly novelty... the real game changer is the big LCD displays like WOZ has. Fortunately when PC sims eventually replicate that style of scoring (on a second monitor), I'm covered.
Anyway, as far as the real DMD, I think it's partially just a perspective thing. To pinheads, adding new toys, color DMDs, etc., etc. is how a lot of guys try to continue getting fulfillment out of machines that in many cases they've had for years on end. To people like me who do not have the luxury of owning any real pins, simply attempting to replicate the nostalgia of the original pins is fulfilling enough.
Now all that being said, if I was building a virtual pin again today, I would probably just stick an LCD in there and be done. There have been several advancements in the virtual pinball world recently that do make it a better overall bet. In the meantime, I'm not ditching my $400 Vishay DMD and redesigning my back box to fit another LCD screen, so I'll hold out hope that Zen will eventually add PinDMD support. They were interested enough in the idea of supporting real DMDs to purchase one along with a PinDMD board. That's obviously no guarantee they'll move forward with it. But if they eventually do, that's great for me and the hundreds of other people that have real DMDs in their pincabs...