Wow,well personally I have found just the opposite in some of my 'convert' friends.They're feeling hungry a dozen times a day because the vegetarian and vegan stuff is so easy to digest.I myself don't know since I've been (lacto)vegetarian since birth.
In general,yes,a vegan diet is lower in fat and if you keep up regular activity level,you'll lose weight.BTW,tofu is good but is also high in fat so it can be bad in excess.

When I became a Pescatarian (vegetarian + fish), I lost quite a bit of weight. We have recently moved to England and I began eating alittle bit of red meat. Well, I immediately gained about 13 pounds, within 3 months. I hate watching my weight, so if all I have to do is cut the meat back out, I'm good to go!

I think that depending on the individual's diet, and what they ate before becoming vegan, people may tend to lose weight. Unfortunately, it is still easy to eat a high-fat vegetarian or vegan diet if you are not careful and avoid treat foods and fried foods. I think that the "full" feeling is usually due to the higher fibre content in vegetables and whole grain foods. This also helps to keep people from overeating as you feel full faster and it takes longer to eat (more chewing). I also think that once a person develops healthy eating habits, junk foods lose their appeal, and can even cause stomach upset.

Here is a link that might be useful: Vegetarian-Tips