This was true when he first went to Man U but after that he rarely produced any players that turned out top quality.
When Wenger and Ferguson were battling it out every season for the top two places, Ferguson was outspending every other club in the PL by more than double.
Just like Mourinho, he was buying squad players for what most clubs would be their record signing.
The main difference between Wenger and Ferguson is that when they won the league Man U would go out and buy even more world class players, but Wenger used to keep with what he had rather than strengthening significantly.
Ferguson was a horrible person but he knew what it took to win, and he did it, even if it meant being underhand about it, and that goes for Mourinho too.
When Wenger first came here he had new ideas and a will to win, he also bought players with the same attitude, but since the Invincibles that has gradually changed and complacency took over.