Use less definitive language for domain sharding

With the rise of mobile (and Google SPDY) it *might* no longer given that domain sharding is still best practice, even though it's still being discussed (mobile: http://www.mobify.com/blog/domain-sharding-bad-news-mobile-performance/) (pros and cons: http://www.stevesouders.com/blog/2013/09/05/domain-sharding-revisited/)