I believe this is how it happens.
Google primarily displays multi link listings when they feel a query
has a strong chance of being navigational in nature. I think they can
determine that something is navigational in nature based on linkage
data and click streams. If the domain is well aligned with the term
that could be another signal to consider.
If you have 10,000 legit links for a term that nobody else has more
than a few dozen external citations for then odds are pretty good that
your site is the official brand source for that term. I think overall
relevancy as primarily determined by link reputation is the driving
factor for weather or not they post mini site map links near your
domain.
This site ranks for many terms, but for most of them I don't get the
multi link map love. For the exceptionally navigational type terms
(like seobook or seo book) I get multi links.
The mini site maps are query specific. For Aaron Wall I do not get the
mini site map. Most people usually refer to the site by it's domain
name instead of my name.
Google may also include subdomains in their mini sitemaps. In some
cases they will list those subdomains as part of the mini site map and
also list them in the regular search results as additional results.
Michael Nguyen put together a post comparing the mini site maps to
Alexa traffic patterns. I think that the mini site maps may roughly
resemble traffic patterns, but I think the mini links may also be
associated with internal link structure.
For instance, I have a sitewide link to my sales letter page which I
use the word testimonials as the anchor text. Google lists a link to
the sales letter page using the word testimonials.
When I got sued the page referencing the lawsuit got tons and tons of
links from many sources, which not only built up a ton of linkage
data, but also sent tons of traffic to that specific page. That page
was never listed on the Google mini site map, which would indicate
that if they place heavy emphasis on external traffic or external
linkage data either they try to smooth the data out over a significant
period of time and / or they have a heavy emphasis on internal
linkage.
My old site used to also list the monthly archives on the right side
of each page, and the February 2004 category used to be one of the
mini site map links in Google.
You should present the pages you want people to visit the most to
search bots the most often as well. If you can get a few extra links
to some of your most important internal pages and use smart channeling
of internal linkage data then you should be able to help control which
pages Google picks as being the most appropriate matches for your mini
site map.
Sometimes exceptionally popular sites will get mini site map
navigational links for broad queries. SEO Chat had them for the term
SEO, but after they ticked off some of their lead moderators they
stopped being as active and stopped getting referenced as much. The
navigational links may ebb and flow like that on broad generic
queries. For your official brand term it may make sense to try to get
them, but for broad generic untargeted terms in competitive markets
the amount of effort necessary to try to get them will likely exceed
the opportunity cost for most webmasters.
Hope this helps.