I don't know if there's any magic bullet in terms of keeping the weight off, but what I like the most about IP is that there's a plan (phase) for each stage and you can move through them as needed. No other diet that I've been on has that. So basically, while I was in maintenance, if I noticed my weight trending up or if my pants didn't fit as they should, I knew exactly what to do to correct that, and I could correct it immediately (assuming I had packets on hand, which I always did).
I think all that any diet can do is give you the tools -- you have to make the hard choices, you have to skip the "bad food", you have to give yourself only one "free day" per week, not 7
What I do like about IP vs. other plans though is that IP is so easy once you get the hang of it (in terms of the rules, not necessarily the behaviors), so that even if you have a lot going on, at least you're not having to add counting calories or adding up points to your daily chores.