At some point, window shadows became much more diffused. I think the release that implemented this change was mountain lion.
I keep a Snow Leopard VM around to occasionally run old software in and the difference in shadow size is always striking. I personally like the more focused look of pre-10.7 shadows.
I just took a look, and I really can't see any difference between the window shadows on my Mavericks machine and my Snow Leopard VM. The Mavericks shadows may be ever-so-slightly stronger.
You may be thinking of Yosemite, which definitely toned down the shadows a bit as part of flattening everything.
I keep a Snow Leopard VM around to occasionally run old software in and the difference in shadow size is always striking. I personally like the more focused look of pre-10.7 shadows.