Why is Nginx more popular than lighttpd?

I'd like to use Lighttpd in production for serving Django apps but i see that these days Nginx is more and more popular. Why is that? I'm aware that in the past Lighttpd had memory leaks but isn't this fixed now? They do have active developers that fix this kind of things don't they?
Is there any reason i should go with Nginx instead of Lighty? I know that nginx is a great server but is it really that good and better than lighty?

I'm a current nginx user and previous lighttpd user and I can only echo the stability issue. Furthermore nginx has active development and often sees a new version released every couple of weeks with new features or minor bug fixes. The configuration file is also quite clear and very powerful once you learn the nginx way of doing things.

Nginx can also be used as a load balancer (although haproxy is probably a little better at this if you don't need SSL).

Nginx can also be used as an SSL reverse-proxy, which is huge if you use SSL on multiple virtual hosts. This is probably the single biggest reason for nginx Netcraft numbers and nginx author said in a recent interview he thought this was the reason for a majority of deployments. It's certainly why I started using it... and then was shocked at the performance gains I was seeing :)

I recently did a side by side evaluation of lighttpd and nginx on the same server for a new project I am working on. Nginx performed slightly better than Lighttpd in my tests, and we have put nginx into production as a result. FWIW Netcraft reports about nginx is much more widely used than lighttpd on outward facing web servers: http://news.netcraft.com/