It's not about the fact that she is making acquisitions. It is a well known fact that CEOs like to be self-aggrandizing by doing big deals.
The difference is the TYPE of deals she is doing.
All of her deals, so far, fit into Yahoo's strengths.
Also...the fact that she is able to do these deals at all, is testament to her genius. Many others before her tried, but couldn't do these deals.
So there must be something different about her than everybody else that tried.
Edit: And yes, the story is yet to be told about how these acquisitions turn out. But with the refocus on product, recent redesign and refactor of Flickr and the way she is consolidating Yahoo's focus around products that give quality display media inventory. That is the genius. It is easy to dismiss it, but if it were so easy, why did no one else do it - including 2 of the founders!
It's what happens after the acquisitions are made that will determine whether Yahoo just blew billions of dollars or actually pushed their company forward into the next generation.