People were nervous because of tapering , syria & the fact that Berkshire has gone from around 90-119.30 in a year. People took a little off. The fact that Hurricane season hasn't been bad so far, and Syria is now on the back burner .Berkshire is less than 5 % from it's alltime high too which hardley qualifies as being stalled .
My guess is it is a combination of valuation and supply & demand. The smart guys who are honest with themselves probably believe that BRK is trading at a fair, or even high, P/BV ratio. Every time a dumb bunny shows up and offers to buy a share at a slightly higher price the smart guys jump at the opporunity to sell that poor sucker their shares. Very simply, the supply of shares that the smart guys would love to unload (sell) exceeds the demand created by the naive, unsophisticated buyers. JMO.