In my previous blog post Taking Profits in Towerstream (TWER), I mentioned that I would reinvest half the proceeds from Towerstream into the gaming industry leader Activision Blizzard (ATVI), making the company not only the largest position in the SINLetter Model Portfolio but also the largest position in my personal (after tax) portfolio.

While I occasionally make some risky trades, for the most part I am a conservative long-term oriented investor with the stock portion of my portfolio spread out between 15 to 25 stocks. Excluding company stock, I tend to keep individual position sizes to no more than 5% of the overall portfolio. Research has demonstrated that the benefits of diversification diminish once you have over 30 stocks in your portfolio. However in the case of Activision Blizzard, I have started building a more concentrated position that I expect to pay off in the next two to three years.

This post is about the key reasons I personally believe Activision Blizzard appears to be an attractive investment and why it now accounts for 13% of the SINLetter model portfolio and 10% of my personal portfolio. My goal is to eventually build this position until it represents 20% of my personal portfolio. Since I have already covered the basics of why I like Activision Blizzard in the September 2008 investment newsletter, here are 10 reasons for making Activision Blizzard a core holding.