1. Very large investors actually don't do anything different. The best game in town is the efficient frontier (modern portfolio theory; essentially, spread the bets around so some zig while others zag). Once you have more than $10 M or so, it becomes worthwhile to start optimizing at the margins; there are things that can be done with tax efficiency that have tiny but real gains, and there are things like exploiting the short rebate and negotiating for special concessions. But as a passive, financially-oriented investor, you're basically playing the diversification game.
2. That said, very large investors almost all get to be that way not by the diversification game, but by the concentration game. Think about the wealth generation period of any industrial fortune: it comes from highly concentrated equity holdings in a corporation undergoing a massive change in valuation (archetypally, profitable growth, although many an investor has done well by changing the valuation through other means, see ESL and K-Mart).
So. The way a person gets super rich is by doing something very different than what you are (should be) doing. And so while they are in that period, their portfolio looks very different. But once they are super rich, if they go to the world's best advisors, they are likely going to get something that looks like a well-diversified asset allocation according to modern portfolio theory.
For most people above $200K income, biggest expense is usually taxes. So it makes a lot of sense for wealthy people to dominantly invest in instruments which has lowest taxes. They take advantage of 15% tax rule for capital gains and also they take massive advantage of real estate sales which are taxed at zero or rates as low as 20%. In addition they can invest in real estate in countries with lax tx policies or where things are very cheap right now such as Italy, Greece and Iceland. Many wealthy also invest in new business projects happening in their social circle. For example, investing another friend's new beach hotel chain or in infrastructure project contract for some government. In these they have advantage that their friends have lot of inside information on how things will go and what are their key strengths, weaknesses and risks. If regular people are allowed to invest in these, they have lot less leverage and no opportunity for timely cash out when things are going to go south. Finally, regular Joe with $100K have far limited avenues for diversification (essentially just stocks and bonds) and even more limited resources for research and re-allocation of assets. Wealthy can literally exercise 100s of options including currency trading, commodities, foreign equities, futures and so on combined with sophisticated call/put options. While a regular Joe probably meets an accountant twice a year, super rich usually have staff of dozen or more in a dedicated office space to continuously analyze and re-allocate assets in realtime. It is not an accident that Bill Gates total networth has more than doubled despite of his massive giving drive and almost a decade long retirement.
Most venture capital funds return between almost nothing and nothing. Most venture capital companies are horrendous stewards of institutional money. You can look up the available data, it's ugly for everything outside the best of the best.
I fail to see how it's worse to take a 97% loss on the bottom 3/4+ of VC firms, as opposed to taking the same total loss on a spread of crowd equity funding investments.