I won't go into detail dissecting what I think the differences and merits are, but...
I became a vegetarian 4 years ago (from a standard western diet) and I did indeed lose weight in the first couple of months, I felt great as a matter of fact. I now believe I went through a detox period. (I had a similar experience when I began eating Paleo.)
My health steadily declined over the years, despite being quite physically active and doing my best to do what I thought was 'healthy'. I lost and could not gain any amount of muscle. Most veggies that I know eventually start to look emaciated and I was getting there. I was scrawny everywhere except my belly and chest, prolly 23-25% body fat. After 4 years I started feeling really poor, mentally and physically, so I started looking for solutions.
Immediately after I began eating quality meat, way more fat, and stopped all grains and sugars, I saw a huge improvement in my mental state and energy levels. After only a bit over a month I'm gaining muscle while slowly loosing fat on my chest and upper stomach. I don't think I could ever go back at this point, I feel like a different person and after a few more months I might look like one.
I guess my point is... sure you can loose weight as a vegan, its even likely, I'd say. But there is a difference between starving your body with malnutrition and eating in a way nature designed your body to eat. Weight loss is not directly correlated with overall health and wellness, even if Weight Watchers wants you to think so.
I don't really buy the idea that some plans are best for some people and others for other folks. There are plenty of diets, even cheesy 'fad' diets will allow you to lose 5 or 15 lbs up front, but I'd bet hardly any of them are really healthy or sustainable for any amount of time. Most of my co-workers are on some kind of fad diet (because they're mostly all overweight) and NONE of them enjoy them. I have not heard from many people who follow Paleo that don't enjoy it. We are all humans and our bodies function 90% the same even after factoring in various disabilities, allergies, diseases, body types, geographies, ancestries, etc.
I think that Paleo/Primal isn't a diet, it's a lifestyle shift back towards where it came from.
K - no more ranting from me... sorry! Welcome! Best of luck to you and know that you have a lot of support around these parts!