Good point about omission of important facts. It's tough because facts can be absent from a news item intentionally and unintentionally. Journalists have time and size constraints - so even when striving for accuracy and objectivity, facts may just be missed and some other known facts will certainly be left out as determined not relevant enough at the time of writing. This is just the reality of reporting news.
Professional Journalism has ethics and standards - of course w/ ongoing debates in how they are practiced - and they are taken seriously by the industry as a whole. Wikipedia has more info: https://en.wikipedia.org/wiki/Journalism_ethics_and_standard...
Ultimately, for news items where a reader wants to get a fuller picture of the story he/she is going to have to go read multiple longer articles about it. Scrubbed bullet points may offer discovery with less bias at this initial stage and from which to choose those stories to go read more about.
I don't want to get off topic, but the Yahoo example mentioned is interesting and I think worth maybe discussing so
TL;DR skip this next part if very wonky Yahoo stock news reporting is not an interest:
Where did you get your Yahoo business news?...Firstly, Yahoo's (YHOO) value is not negative ex Alibaba (BABA). "A company's shares are worth what someone is willing to pay for them" is a relevant quote here and Verizon offered ~$4.8 Billion to buy Yahoo ex Alibaba (also ex Yahoo Japan btw).
Pretty big difference between a negative value and $4.8Billion!
Second, if talking about a stub Yahoo valuation? Like using some shorthand value estimation method based on looking at: (BABA's recent stock prices)x(size of Yahoo's stake) and comparing that amount to where YHOO's market cap is trading at? Then yes you could end up at all kinds of crazy totals, including negative numbers, depending on what shorthand valuation method you chose to use...
But these types of calculations, maybe interesting and fun, are basically meaningless in the real world. The amount Yahoo will receive for its Alibaba stake at some unknown time in the future cannot be calculated accurately from BABA's stock price today. Nor can it derived from whatever $ amount Yahoo has written in its books for the value of their BABA stake (Book value market value). (Sum of parts also market value)
Yahoo can be trading at a discount (or a premium) to one's hypothetical future value calculations for all kinds of reasons: eg YHOO's potential +$10B tax liability uncertainty should they sell their BABA shares with capital gains (Yahoo still talking to IRS about this and its unclear how it will play out but it's shocking Yahoo has not been given clearer answers by the IRS yet to quite fair questions about the tax code)
Yahoo is also still facing material issues in Verizon deal not yet finalized (YHOO email breach may change terms, this is also unclear), etc.. etc..
Basically, Stock Valuation Is Not News. Though some stock trading websites look like news or are attached to legit news sites (Barron's to WSJ for example). Barron's is not news.
NYTimes DealBook discussed Yahoo stub being negative. DealBook is a blog. http://www.nytimes.com/2015/12/10/business/dealbook/how-to-v...
An analogy for those not familiar with Yahoo's stock price valuation: This is like guessing how much money you could receive from selling your house if you tore it down and sold it for scrap wood and separately put the plot of land on the market. You also have to calculate this future value without knowing if your local council will approve the idea, or how long it will take, or what prices for scrap wood/plots of land will be, or how much tearing down your house will cost, or the % odds you secretly have been living in a house built over an old unicorn graveyard and can't sell the land at all.
One can imagine all these factors are why a number calculated for future "value" of stock may be very different than what actually is received when a sale happens. Like way off. Like a negative number vs. +$4.8Billion way off.