Seems that if you do a search while in metro for font then click on settings and select make everything bigger you will affect the metro interface whereas if you do it in the desktop you get the desktop settings.
Quote from where I found that
"With the largest population cohort in recent history hitting the age of vision deterioration, and with all kinds of new technology, MS ought to seize the chance to really serve a population.
We're also the people who latched on to the PC and have used it fanatically for 30 years.
Now you're going to jam us between finger-painting (Metro) we don't have equipment for, and text we can't read????"
They should consider how the whole touchscreen visual interface craze has made things somewhat more challenging for the Blind.