Artificial demand: created by others or in your own head or in this example, both. I don't mean to be negative, but this seems like a lot of http://en.wikipedia.org/wiki/Bread_and_circuses to me...
I think a lot of people just like the clean, minimal look. That's why they install the WP theme, not because they're jealous of whatever artificial scarcity/demand hack is actually driving the original Svbtle network. Is there really a reputation boost by virtue of being an actual member?
Check out https://simvla.com for an open-source / "non-exclusive" alternative!