Being vegan helps me keep my weight under control not because plant foods are necessarily healthier or less fattening than animal products. It's because being vegan helps me resist "mainstream" treats when I'm outside my home. If I were vegan strictly for health reasons it would be much harder to summon the willpower, but having other reasons makes it easier to say no to sweets containing dairy and eggs.
I don't feel deprived, though, because I live in San Francisco where there's an abundant supply of vegan treats. boyziggy and I have agreed that it's easier to say no to a slice of nonvegan cake at a party when we know we can get one just as good at Ananda Fuara or Source. Dark chocolate without dairy is not difficult to find; my sweetie Ben introduced me to the most wonderful chocolate I'd ever tasted, from Poco Dolce (available at Whole Foods Market). And there's always mail order; Ziggy often orders me birthday and Valentine's treats from Chocolate Decadence.
Sure, all these things are less convenient and more expensive than grabbing a random candy bar at the corner store, but that's kind of the point; special treats should be just that, special.