Phew, what a marketing brainwashing!
You see, nginx haves no trouble to saturate 1Gbps link on common desktop hardware and would do 10Gbps at decent server hardware, leaving a plenty of resources for other tasks, granted that other I/O like HDDs could keep up with such speeds. So in fact if you dont do things horribly wrong, in real world you would end up being I/O limited anyway so no way to gain more than that without further upgrade of hardware, etc :p
Not to mention Nginx features very cool cache system which could make a day if you're slashdotted. You see, serving static copy is almost instant. Running PHP (or whatever) script is not. This way, an average cheap hardware could easily withstand slashdot effect.
And yes, it comes with source. So I have it everywhere. Up to my ARM based NAS and MIPS based router, where low resources consumption counts 10 times as much as on x86.
p.s. lack of source implies vendor lock-in and inability to choose OS and CPU arch except those "approved" by ppl who builds blob. And ton of other artificial restrictions. That's just stupid. FAIL.