No, they tried to build the app with a technology they wanted to learn {Reddit : Lisp, Twitter: Rails} and then had to rewrite it (mostly) from scratch when that didn't work out {Reddit: Python, Twitter: Scala}.
Neither failed, because they were smart enough to know when to ditch. God knows how many startups failed because they didn't know that.
For Twitter, Rails was the technology they knew. They decided it wasn't the right tool for their needs. Scala is the tech they learned (and continue to learn) on the job. They even have a group blog detailing this process (http://gracelessfailures.com).
Neither failed, because they were smart enough to know when to ditch. God knows how many startups failed because they didn't know that.