It depends on your measure. It could be argued that it's not undue weight as these sites have impacted on such a massive proportion of the world's society. For instance, gcc and unix didn't allow for the sort of direct communication that twitter caused - look at the Arab Spring for example.
That the technologies you mention enabled the websites mentioned is not in doubt, but without the websites and related technologies would things like TCP/IP and Unix have had such an impact?
Seems that my comment is controversial as someone has voted me down. I'm curious to hear from opposing views - I love technologies like TCP/IP, gcc, Unix, C, etc. - but I think they wouldn't be much use unless they were used to enable applications like Twitter, Google, Nethack and Wikipedia.
I do want to clarify that I'm not saying that the underlying technologies aren't amazing.
I think the debate is whether TCP/IP would be useful without Google, or Wikipedia would have happened without TCP/IP. Personally I would say that IP changed the way people think about information, which made Wikipedia seem plausible.
That the technologies you mention enabled the websites mentioned is not in doubt, but without the websites and related technologies would things like TCP/IP and Unix have had such an impact?