<p>According to a SO meta post from 2010, the results returned when asking a question are simply from searches with "intitle:1" added to the query ( <a href="https://meta.stackexchange.com/questions/39362/why-does-intitle1-show-questions-whose-titles-dont-have-all-my-search-terms">Why does intitle:1 show questions whose titles don&#39;t have all my search terms?</a> ).  However, the "intitle" operator appears to have been deprecated.  Another 2010 SO meta post suggests pre-pending a query with "title:" will return results more similar to the "ask a question" search.  For example:</p>

<ol>
<li><p><em>what is confounding</em> <a href="https://stats.stackexchange.com/search?q=what+is+confounding">https://stats.stackexchange.com/search?q=what+is+confounding</a> returns 4,981 results.</p></li>
<li><p><em>prepend intitle:1</em> <a href="https://stats.stackexchange.com/search?q=intitle%3A1+what+is+confounding">https://stats.stackexchange.com/search?q=intitle%3A1+what+is+confounding</a> returns 4,981</p></li>
<li><p><em>prepend title:</em> <a href="https://stats.stackexchange.com/search?q=title%3Awhat+is+confounding">https://stats.stackexchange.com/search?q=title%3Awhat+is+confounding</a> returns 950 results, which seem to be mostly in the same order as typing "what is confounding" into the ask a question page.</p></li>
<li><p><em>prepend title: to each term</em> <a href="https://stats.stackexchange.com/search?q=title%3Awhat+title%3Ais+title%3Aconfounding">https://stats.stackexchange.com/search?q=title%3Awhat+title%3Ais+title%3Aconfounding</a> returns 940 results.</p></li>
</ol>

<p>I'm not sure what the technical difference is between 3. and 4., probably slight differences in the weighting, but the results do not differ enough to justify prepending "title:" before each term.  More information on advanced search operators is available: <a href="https://stats.stackexchange.com/search">https://stats.stackexchange.com/search</a></p>

<p>And some more discussion of SE search from the blog:</p>

<ul>
<li><a href="http://blog.stackoverflow.com/2008/10/stack-overflow-search-now-51-less-crappy/">http://blog.stackoverflow.com/2008/10/stack-overflow-search-now-51-less-crappy/</a></li>
<li><a href="http://blog.stackoverflow.com/2009/07/stack-overflow-search-now-61-less-crappy/">http://blog.stackoverflow.com/2009/07/stack-overflow-search-now-61-less-crappy/</a></li>
<li><a href="http://blog.stackoverflow.com/2011/01/stack-overflow-search-now-81-less-crappy/">http://blog.stackoverflow.com/2011/01/stack-overflow-search-now-81-less-crappy/</a></li>
</ul>

<p><strong>To summarize:</strong></p>

<p>Someone with a better understanding of the inner workings of search on SE is needed to provide a definitive answer. However, the probable reason that you have more success with the "ask a question" searches is because they are more limited in scope, searching only question titles. The main search function, while it gives more weight to hits in question titles, still returns many more results that have the query in the body of questions and answers.  Incidentally, I think the main search tends to ignore comments.</p>
