This theory has been in the back of my head but I never really expressed it before, so bear with me.
Cobb was always confident in the reality in which he lived. That is why he wouldn't jump with Mal. He knew that it was all real without a doubt. After Mal's death I think spinning the top became a habit because he hoped it was a dream so that he could return to Mal. His connection to Mal is what made him question his reality. When he was finally able to put his guilt about Mal behind him and accept her death, his natural confidence in his reality returned and thus he didn't need the totem to tell him whether it was a dream. The top kind of represented Mal to him, it was hers and it was because of the top that she died, with little hope of ever seeing his children again the top became his only connection to his family. He no longer needed this connection and he never really needed the top to confirm his reality and thus he ran to his children confident that they were real.
Not sure how much of that made sense, but I hope you catch my drift.
Cobb was always confident in the reality in which he lived. That is why he wouldn't jump with Mal. He knew that it was all real without a doubt. After Mal's death I think spinning the top became a habit because he hoped it was a dream so that he could return to Mal. His connection to Mal is what made him question his reality. When he was finally able to put his guilt about Mal behind him and accept her death, his natural confidence in his reality returned and thus he didn't need the totem to tell him whether it was a dream. The top kind of represented Mal to him, it was hers and it was because of the top that she died, with little hope of ever seeing his children again the top became his only connection to his family. He no longer needed this connection and he never really needed the top to confirm his reality and thus he ran to his children confident that they were real.
Not sure how much of that made sense, but I hope you catch my drift.