The second question I received from my SEO Questions & Topics: Reader Feedback Requested was;
Do you think google manually add sites in top 10 for competitive keywords?
If you want to know what I think, personally.... Well, I do not think Google manually adds sites into the SERPs based on it being competitive or not. I do think they adjust the algorithm to ensure the sites they want in the top 10 for certain keyword phrases are there. But I do not think they manually stick a site in.
Do they pull sites out? If they are "spammy" they will. If not, they may adjust the algorithm to knock them out.
All in all, I think for the most part, Google keeps it automatic and does not use manual means to have the "most relevant" results in the top 10.