If Google understands the content it's presenting, like weather, it will read it out loud to you. If a wikipedia article is the first result, it will read the entire first paragraph out loud.
google now will try it's best to answer questions out loud if they were asked that way. Your weather example works, but in general it's inconsistent enough that i can't assume it will give me an audible answer, and I usually limit myself to speaking only questions or commands that i know to work.
Re:Amazon Echo Released
by dragonwriter on Tuesday June 23, 2015 @12:47PM
(#9765847)
> google now will try it's best to answer questions out loud if they were asked that way.
And its a fairly amazing technical achievement, but its still got a long way to go -- if you ask when a business opens, it will show you the hours but not tell you the time it opens, even though Google has enough semantic understanding of the open/close times to tell you on the results page with the hours that it is "closing soon" or "closed now" if that is the case.
One of the things with Echo is that it doesn't have a screen, so everything has voice responses.