D&D has almost always been the main gateway to RPGs, and when it suffers, there is the long-standing feeling that the whole RPG industry, such as it is, suffers.
But, I do think that in the later 90's, Vampire and WOD reached a point were they could also do new player acquisition, and had some advantages in new player acquisition.
Yet, I do not see one person here that came in through Vampire on this thread, so I could be wrong. Or they just wouldn't be on these boards.
I actually first came across the idea of an RPG in a Hardy Boys book when I was about 7, and I was enthralled by the concept. I actually wondered whether it was real, or whether the author had simply made it all up. Taking inspiration from the Game Boy game, Final Fantasy Legend, I set out to create my own RPG. I hadn't the first clue as to how to design a game though, so it didn't go far beyond some drawings in a notebook that had Attack and GP values arbitrarily assigned to them.
A year or two later, I finally found a hobby shop that carried D&D, and I convinced my mom to buy the black box for me. So that's where I officially got my start. However, for the next 10 years I'd have a lot of trouble getting a stable gaming group. I played maybe once or twice a year on average. A disproportionate amount of my time was spent reading a variety of RPG books and working on my own material (most of which never saw the light of play).
Among the books I owned was Changeling, but I had avoided Vampire because I had gotten it into my head that Vampire was for goths (and I wasn't). All of my friends knew that I gamed, and while we were hanging out at a pool hall one day, one of them struck up a conversation with a guy who invited him to a Vampire larp. My friend said he wasn't interested, but pulled me into the conversation since he thought I might. I had my reservations, but ultimately decided to take a chance and I went.
I ended up enjoying larping Vampire, though I still much prefer tabletop RPGs. More importantly though, that larp lead me to meeting some folks who became a long term D&D group (several of whom were groomsmen at my wedding). We also played a number of other games, but it was usually D&D, often 2-3 times a week.
So, finally getting to the point. While D&D was my first RPG, without Vampire I would have probably never met my main gaming group. Without them, it's hard to say whether I'd even still be part of the hobby.