It's been a good year to be a BlackRock ( BLK) shareholder. Shares of the asset management giant have rallied almost 34% year-to-date. That shouldn't come as a huge surprise, though -- BlackRock is the biggest investment manager in the world, with $3.8 trillion in AUM. As this rally keeps propelling stocks in 2013, it's also inflating BlackRock's revenues along the way. Last quarter, funds increased their collective stakes in BLK by 37%, picking up another 37 million shares. That makes funds' total position in BLK worth more than $35 billion right now. >>5 Rocket Stocks Worth Buying This Week BlackRock owns an attractive business right now. Because its clients are predominantly other institutional investors, BLK boasts stickier revenues than more-retail-focused peers. That's not to say that retail investors aren't an attractive client base for BlackRock. The firm's still-limited exposure to retail business gives it a big opportunity in the years ahead, especially after its game-changing acquisition of Barclays Global Investors. Another shift from the BGI purchase is increased exposure to equities (before that, BlackRock was known for being a fixed income shop). Since stocks come with higher management fees, bigger AUM in equity means bigger revenues for BLK. New changes in investment fund regulation have been good and bad for management firms lately. The SEC loosened marketing restrictions on hedge funds, which BlackRock markets to its clients, while tightening money market fund restrictions. Ultimately, the rule changes are a small net gain for BLK, but it could become a bigger impact as more investors opt for alternative investments over fixed income in this low rate environment. So far, professional investors' bet on BlackRock appears to be paying off.