1. It could be natural link growth. Often when a webmaster links to you they will do so using your brand name or a URL.
2. All links to a domain increase the domain authority. It could be that they have strong domains which outweigh the need to have exact match anchor text. This is especially true if they're big brands- think about how Amazon ranks for so many products without actually having links to those product pages.
3. That's a strategic decision that varies depending on your site's circumstances. New site with no links = build branded anchor text. Old site with lots of branded anchor text already = build some exact match anchor text (but not too much obviously).
4. Focus on branded anchor text BUT throw some love at your product pages occasionally as well. You'll probably be able to drive some long tail traffic just by virtue of having unique content on the page and as your domain authority grows this will not only increase long tail traffic but also rankings for those exact match term.