What's so hard about saying, "I love you?"

Matthew has proved himself to be a typical male. What is it about that Y chromosome that causes such difficulty in expressing emotions directly?

Yesterday, I said, "I love you Matthew!"

"I too," he replied. "High five!"

Can't you just see a 20 something man replying this way to his girlfriend? "I love you," she says.

"Yeah, totally," he answers. "High five!"