You heard it from the Man first:
Joss in the Hush commentary:
"When you stop talking you start communicating."
"The idea that language because it is so specific and constrictive can interfere with actual communication."

When I heard that I thought to myself, "Omg, the man is a genius." My point is that Oz, through using less words, what he actually means comes across loud and clear.

Try it. Instead of giving a complicated speak about how much you love your someone, just touch their hand, kiss them, or give them a meaningful stare to show them how much you love them.

I think the Willow/Oz relationship was so cute because when Willow was worried, Oz would just make the slightest gesture to comfort her (whereas Angel would give Buffy a long, thoughtout, ahem...boring speech).

Xander: (re. Oz)
It's more a verbal nonverbal. He speaks volumes with his eyes.

Buffy:
"Oz... You okay? If it's possible, you seem more monosyllabic than usual. "

However, when Oz does say something it is very direct and profound.

Oz: We attack the Mayor with humas.
A profound classic.

When you don't normally talk alot, what you do eventualy say becomes more exaggerated. It is almost like the boy who cries wolf. (From my own experience) when you talk alot people start to tune you out. But, when someone like Oz interjects an obscure statement people are more apt to listen to you.
Here's the tip if you are feeling ignored: Stop talking, then when you do say something people will listen.

As quoted in "The Quotable Slayer"
Oz: We talked all night.
Willow: I used to tell people we did that sometimes, but nobody believed you knew that many words.
New Moon Rising