The content may keep coming up because the individual user pages do show the non-obscured content linking back to the parent question.

Observe, please...

I made this search :

https://www.google.com/search?q=python+vs+php+quora

And got a topic with answers obscured.

http://www.quora.com/Python-programming-language-1/Which-is-...

I then selected a portion of the obscured text and made this query :

https://www.google.com/search?q=python+vs+php+"Here are just a few reasons based on my"

Came up with the original obscured answer on that very same question :

http://www.quora.com/Python-programming-language-1/Which-is-...

Check out that page's source. You'll note the canonical URL is the original question.

  <link rel="canonical" href="http://www.quora.com/Python-programming-language-1/Which-is-better-PHP-or-Python-Why" />

Since Googlebot will dutifully obey canonical, we now have link-bait to the original question with obscured content instead of the non-obscured answers. Again, this is gaming the system. You may disagree, and Quora may as well, regardless that's what's happening.

Edit: Link to webmaster guidelines on rel="canonical" :

https://support.google.com/webmasters/answer/139394?hl=en

   Adding this link and attribute lets site owners identify sets of identical 
  content and suggest to Google: "Of all these pages with identical content, 
  this page is the most useful. Please prioritize it in search results."

Quora is gaming the system. Period. I won't pursue this point any further.