Although the immediate reason BRK/B ended up in the S&P 500 was because they acquired BNI (Burlington Northern, a railroad company) for stock in 2010. But fair enough that it wasn't in there beforehand and is still around now. I don't remember why, probably some other S&P decision about the big-numbered, less liquid BRK/As.
Also, BRK/A shares are quite expensive but you still get Buffett's shareholder reports with a share of BRK/B. I'm sure you could find them either way, but hey. Interesting reading is a nice fringe benefit.
