I am wondering how open google update links and what is the density of back link interms of google SERP. I have seen site that rank in top 10 with no back links...
Lots of factors involved and no one outside Google knows for sure. Matt Cutts has explained last year that Google would be in a state of everflux. They are updating all the time and SERPs are changing all the time depending on the DC that you default to. As for your top 10 site with no backlinks, I guess it really depends on the search term. If you are top 10 on a rare phrase, I wouldn't think much of it. If it's not so rare then it probably won't last long, so enjoy it.