Sitelinks are more common these days. Popular blogs and websites have been awarded Google sitelinks recently. Google’s explanation is that this is a completely automated phenomena and there’s nothing one can do do help the sitelinks appear for his/her site on the Googel SERPs.
Daily SEO blog has a sitelink and there are some random links on it. See screenshot.

Now, what appears on the sitelinks is completely up to to the Google bots to decide. I can’t see a definite pattern on the links appearing on the sitelinks but yes one of the factors that decides it is the “Popular searches”.

I’ve found from my referral codes and content popularity checks on Google that the pages to which Google has placed the sitelinks are the most popular pages on searches from Google.

Example, Upcoming tech bloggers in India is a post whose content has traveled lot in the blogsphere, and was visited most through search engines and other sources (IM, Email etc). It has some backlinks too (acquired quicker and naturally).

So I think for a link to appear on sitelinks (or sitelinks to appear for that matter) the factors Google would consider are,

1. Popularity of the article/page
   Popularity is considered as the number of times the article has been accessed from the site. Obviously the sitelinks are the ones that are the most popular on that website.
2. Natural link bait or not
   Link bait might be the wrong term for it. But yes, it’s something similar. For an article to get featured on the sitelinks, it might need to be linked most from other websites, at a quicker pace and naturally.
3. Search friendliness
   Another criteria believed to be taken into consideration for a page to be included in the sitelinks is the measure of it’s search engine friendliness/ likeability.
   It can be measured as the number of times the particular article was “searched and clicked on” through the search engines.

Now, what is some page crawled up the sitelinks which you does not want to appear on the sitelinks? What can you do to control the links that appear on the sitelinks?

Here’s what you do.

1. Register at Google Webmaster Central – It’s a shame if you have’t already. Do it now.
   
2. Goto Dashboard > Links > Sitelinks
3. If you have a sitelink, Google will show the existing links for the sitelink and the “block” option
4. Click “block” for those link you think are unnecessary.

That’s it. So even though you don’t have the access to decide what links appear on the sitelinks, you have the access to decide as to whether they should appear or not.

Related reading on Sitelinks at DailySEOblog Article 1,Article 2,Article 3