techmeme and digg are two of my favorite web sites. Diggers are clear about digg’s rule: if the numbers of diggs is big enough, the article will be shown on digg’s front page. Therefore, people can game digg. On the other hand, techmeme‘s algorithm is not published. People have no idea whether their post will be shown on techmeme.com.
Personally, I find posts on techmeme.com is more useful than posts on digg.com, though I find more fun on digg: once you digg an article, you are eager to find if there more people digg it too.