Part of what I think is fundamentally different about the two is how McClusky punched Micheal in anger. Vito never would have done that. In fact, he wouldn't have wanted his enemy to know he was angry. At least not until he was taking his revenge. McClusky was more of a hot head.

Also, he wasn't very observant. Notice how (both in the book and in the movie) in the restaurant he's so into the food instead of what's going on between Solozzo and Micheal. Granted, he couldn't understand Italian. But if the movie is any indicfation, one look at Micheal's face and both men should've known that something was wrong. Solozzo at least showed suspicion when he frisked Micheal in the restaurant.

I doubt Vito Corleone would've let that slip his notice.