Marissa Mayer is possibly the best thing that has happened to Yahoo!
She has also started an initiative to get back "old yahoos" who has left (I am waiting for my phone call, Marissa, if you are reading this, give me a call, theres a dear)
There is another issue with working from home that has to be dealt with, and that is the possibility of security breaches. People working from home has access to a lot of Yahoo! back end systems, and you really dont want them outside the corporate network, but within the security of the building.
LinkedIn, Twitter, Facebook has all experienced hacking and security breaches, I imagine she is keen to tighten security too, to prevent further security breaches.
To be perfectly honest, I would prefer an engineer who has access to the back end of my email account to work from an office, and not in some obscure living room/shed out in gooblediville.
"A lot of people, especially women, at Yahoo will no doubt have taken the job because they can do it from home."
I honestly doubt this is the case. Even when I was working there some of the engineers had such revered status that nobody said anything when they did not show up at the office. In the end it was rare for them to be in. I have a feeling this is the culture she is trying to clamp down on. I might be wrong though.