Related: I generate an "Ask Hacker News Weekly" listing by scraping /ask the same way as my "Hacker News Daily" scrapes /news: http://www.daemonology.net/hn-weekly-ask/
While I think they actually are doing minimal stemming, those are key terms that an index for this site absolutely should include in their index: even if every other two an three letter word is thrown out, "ask" and "hn" should not be.