There's simply no valid reason (and hacked in a weekend doesn't cut it) to store units in Imperial, let me choose, as as an engineer I abhor laziness in building such sites, in 2012, more than ever I18n and L17n are more important than ever, even within sites only offered in English language.
(plus the maths on converting weights is more sane with metric units, I just don't get it)
Whilst creating an application that deals with different units is not a massive amount of extra work, launching a minimal viable product to 300 million people in a country that has a major obesity problem is probably not a bad start. And when I say not a lot of extra work, 2-4 hours depending on experience of units, server side and client side, data store, would be very optimistic, hundreds if you are moving towards a more complex project. Quite a bit on top of what was only a weekend project.
The issue I see is that you aren't going to get publicity like this twice. "We now support metric" isn't news that will show up on my radar in the same way that this announcement did; how many will bookmark this and check back later, if it doesn't work for them now?