I'm going to back up your "So What?" with another point of view.
There is a perception that traditional "big business" has long understood, but that the big Internet corps like Yahoo and Google have yet to "get", and it holds that the less you focus the worse a job you will do.
Corporations like Procter & Gamble have solved the problem with heavy branding: Tide, Bounty, Charmin, Crest, Oral-B, etc., etc.
Each brand exists as if it's a complete and separate company. While I doubt there's many people who haven't heard the name "Procter & Gamble", most people use their products without realizing that they're using a P&G product. Some P&G brands might even compete against each other.
There is no reason that Yahoo needs to "glue" it's products into some sort of "Yahoo identity." In fact, if the Yahoo! "brand" is dying, they could opt to kill it off entirely and go the branding route. Keep Flickr as "Flickr" and Tumblr as "Tumblr." They're solid brands unto themselves. I think that even gives Yahoo an edge because people, psychologically, become more likely to use something that stands on it's own rather than gets package-dealt with something else. For example, psychologically people tend to think "If Yahoo Search sucks then Yahoo sucks and so 'Yahoo Flickr' must suck too." Keep the branding separate. Flickr = Flickr, Tumblr = Tumblr and then only people who are really passionate about their reasons for liking or disliking specific corporations will care that Flickr and Tumblr just happen to be owned by Yahoo.
Google has a really good thing going with Youtube, as a brand, and should *not* try and integrate it with the Google name in any way. Notice how many steps in that direction have resulted in negative blow-back. Like trying to force people to use their real names for comments, and link their Youtube accounts with a Google account. I used to have a registered Youtube account, I don't anymore because of that. Gmail was a success story, and in some ways it might qualify as a brand unique from "Google", but people think of "Google" as a search engine. They'd be better off keeping it that way. Blogspot should stay Blogspot, Chrome should stay Chrome. There's no reason not to drop the "Google" name from each of those brands entirely and let them stand on their own. While this is pure conjecture, I kind of suspect that Google Plus may have had a slightly better chance of succeeding as a Facebook killer if they had done a better job with branding, and not associated it with Google. It should have focused entirely on what separates it from Facebook and makes it *unique and compelling* instead of "Hey Google has one too!" ... the appropriate response to that was "so what?"
Apple is a total anomaly in the world of branding. They've created an "Apple Identity" and their indivdual brands have been able to benefit from that. But it also puts their individual brands in potential jeopardy becuase if the Apple brand takes a hit it's more likely to trickle down to their individual products.
Yahoo could be very successful as a holding company with many unique brands that each focus on their own individual "identity." They don't need to integrate a thing or attach the Yahoo name to any of them. Just let each product shine on it's own.