They've got at least three different programming ecosystems thrown together it looks like. Admittedly some of it may be legacy, but still most large environments I've had experience with have a bit more focused an approach. The more different moving parts you have, the more different things you have to head-scratch at when something breaks and you get a 3am page. ;)

Yeah, I could see a personal project using a good chunk of those. (Apache, nginx, memcached, MySQL, Varnish, PHP) It's definitely not outrageous to think Tumblr uses them all.