Is this purely a function of sharding liability across a conglomerate of businesses? It seems like concentrating Google's ad revenue in a smaller, more efficient business unit is a nod to Berkshire Hathaway's method of business. I can't recall this sort of thing happening in my lifetime, so it will be really interesting to see how this plays out. I also wonder how this would be treated if Google didn't have the crazy…
Berkshire is composed of pre-existing businesses that were themselves successful before being purchased. They are not experimental ventures that need to be subsidized. It is exactly the opposite: money is plowed into the strongest businesses. They each generate excess cash, and it is easier to reinvest that cash in some places than others. The conglomerate structure makes it possible to put the cash where it gets the best returns without having to pay taxes or transaction fees.
Alphabet has none of these properties, except the ability to allocate capital tax-free, but they already had that as Google.