Well sometimes it is needed to not only play consistently but have luck when it comes to a breakthrough. Nole certainly hasn't played that much against "good players" on his way to reach top 10. That is his luck. Even if his luck had still existed, he could've missed his chance, but he took it. That is his consistency.
However, although he's reached top 10 currently, we never know in the future. We should aware that Hewitt and Safin reached No.1 in ther world quicker than Roger.
One more thing, right now there are so many jokes in the top 10. But I won't count Nole is one of them even though sometimes I call him Joke only because I don't like him