Speed still irrelevant in many applications.
Maybe is fine if you have a controlled traffic, but with better speed you can manage more traffic with the same hardware. That's why Facebook had to build a PHP compiler at some point.
In any case, How you would justify using Ruby over another script language like Python, Perl, etc? All of them are comparable in terms of productivity and seems to be orders of magnitude faster.
I'd recommend Ruby because it's readable, it has a good tool ecosystem a great community and design decisions that please me. Python and Perl are just not what I'd like to see in a language. I will use them if I have to, but given the chance I'll use Ruby.
Exactly how do you know what the majority of applications do or don't do?
Besides, code is written for more than just websites. Chef/puppet/cfengine, one-off scripts you write, etc. There's a whole lot of these types of things that don't matter if your code takes 0.01 seconds or 0.05 seconds.
"There's a whole lot of these types of things that don't matter if your code takes 0.01 seconds or 0.05 seconds." Yeah but why would you prefer Ruby instead of PHP/Python/Perl for those things then?
Edit: And when I actually need better performance from a specific piece of code, I can and do drop down to C.