Peggy Noonan has an excellent article over at the Journal:

Mr. Bush is the triumph of the seemingly average American man. He's normal. He thinks in a sort of common-sense way. He speaks the language of business and sports and politics. You know him. He's not exotic. But if there's a fire on the block, he'll run out and help. He'll help direct the rig to the right house and count the kids coming out and say, "Where's Sally?" He's responsible. He's not an intellectual. Intellectuals start all the trouble in the world. And then when the fire comes they say, "I warned Joe about that furnace." And, "Does Joe have children?" And "I saw a fire once. It spreads like syrup. No, it spreads like explosive syrup. No, it's formidable and yet fleeting." When the fire comes they talk. Bush ain't that guy. Republicans love the guy who ain't that guy. Americans love the guy who ain't that guy.

Someone said to me: But how can you call him normal when he came from such privilege? Indeed he did. But there's nothing lemonade-on-the-porch-overlooking-the-links-at-the-country-club about Mr. Bush. He isn't smooth. He actually has some of the roughness and the resentments of the self-made man. I think the reason for this is Texas. He grew up in a white T-shirt and jeans playing ball in the street with the other kids in the subdivision. Barbara Bush wasn't exactly fancy. They lived like everyone else. She spoke to me once with great nostalgia of her early days in Texas, when she and her husband and young George slept in the same bed in an apartment in Midland. A prostitute lived in the complex. Barbara Bush just thought she was popular. Then they lived in a series of suburban houses.

Bush is a normal guy, who doesn't speak fast, well, or with big words, maybe that's why people like him.