Does anyone think that most peoples devotion to Snape is because he was picked on?

No, I don't think that's the reason. I think they liked how he was so mysterious, and in the end, a 'hero'. I say 'hero' maybe because I don't like Snape much. Yes, his actions were very heroic. If Voldemort found out he was a spy, he could have died... Earlier than he did. He put his life on the line. That can't be denied. But the way he treated Harry & the rest of the Gryffindors was not right! Harry might have looked like James, but he was not James! If he put the bitterness of his past behind him, and was somewhat of a nice guy, maybe I'd like him.

Way I see it, there're five categories of Snape fans:
- those who think he's hot
- those who think he's a hero
- those who feel sorry for him
- those who identify with him a lot
- those who are two or more of the above

so, yes.

I think it's a combination of 3 factors.
1. Pity. The reason you mention - being picked on - is part of this. Also his early childhood.
2. The courage it'd take to spy, and the way he died.
3. They think that him loving Lily for years "always" is really romantic.