What the market is essentially saying is they don't agree with Bloomberg analyst's or others' evaluation
of the value of these other companies. The natural conclusion is the market says THE ANALYSTS ARE WRONG
in their estimates of the worth of Yahoo Japan/Alibaba.
It is the analysts, not the public that assume it is the US portion of Yahoo's operations that are being valued at $0.
By the way.... just because some Alibaba stock or some Yahoo Japan stock is available on other exchanges
at a certain price; does not mean the entire company is valued at the current marginal price of stock trades.
That is a form of extrapolation which is subject to large errors. The market valuation of Yahoo US based on price of individual shares is also an extrapolation.
One should not assume that all the outstanding shares in Yahoo are available for the same price,
to an investor possessing current marginal trading price in $ per share times number of shares, in cash.
That doesn't really tell you what the market will value the company at, perhaps as a rough estimate with errors between 10x and 100x.
It is just the analyst/reporter's underhanded way of saying -- since we're infallible about the proper valuation
of these quickly growing portions, and nobody else could possibly ever see any differently -----
any difference in US stock price must be attributed to negative value from the slower growing portion of the business.
Maybe it's just that their other non-US operations are being assigned a discount,
for various reasons, below what the analyst wants to value them at.