Wrangler sales have skyrocketed in the past few years because of the JKU. The 4 door version made the Jeep a practical vehicle for non-offroad people and I believe that Jeep had to make the 4 door to keep Wranglers relevant. How many 2 door JK's do you see driving around? In my opinion, there are two types of Wrangler buyers, a small amount are off-road enthusiasts and a larger amount are people who want to look cool in a Wrangler. People are going to start to realize that buying a Wrangler for daily driving makes no sense once the "coolness factor" wears off. Therefore, Jeep will have to make the Wrangler better for daily driving.
No one can argue that the 4 door Wrangler is what really put the Wrangler on the map for the masses. You hardly see 2 door models, and with the new JLs, they even delayed the release of the 2 door model until after the 4 door, and I have no doubt whatsoever that this is because the 4 door drastically outsells the 2 door.
I'd bet dollars to donuts that if Jeep had never introduced a 4 door Wrangler, the Wrangler wouldn't be nearly as successful now as it currently is. I'm not saying they wouldn't sell 2 door models, I just mean it wouldn't be on the level that it is with the 4 door models.
Like you said, the 4 door made the Wrangler an accessible vehicle for almost everyone, whereas the 2 door had a very limited market by comparison.