So one checked with his Schwab account. In their case, we learned that Schwab offers fractional shares of any stock in the S&P 500. But since BRK is only represented by the B shares in the index, they do not offer fractional shares in the A stock.

Interesting.
I checked, and it's a similar problem at Interactive Brokers.
They have a long list of eligible shares - over 12000 tickers - but not BRK/A.

So, oddly, the share that one would most likely need to have a fractional purchase isn't available for fractional purposes.
At those brokers, anyway.

There was a comment a while back about the rising A volume, and another poster (forget who) suggested it may have been due to quirk in how fractional shares are reported.
So it's an interesting question whether ANY brokers are offering fractional A shares.

It seems like my speculation as to the reason for rising A volume doesn't wash.
Something is sure causing the reported volume to rise. The one month average reported volume is 6.5 times as high as it was 2 years ago, and it has been a steady climb.
The one-month average reported is 8% higher than a month ago, 15% higher than two months ago, 34% higher than three months ago, 49% higher than four months ago, and so on.
I wonder what it is?

Jim