I do't think they have any bigger personalities than straight men - but a lot of women are happy in their company because they know they're not going to come on to them.
Not all of them.. My two best friends are guys.. one is gay and the other is bi. Both are big characters but I don't think it's down to who they go for! lol!
Some gay guys have big personalities and some women flock around them. Some straight men have big prsonalities. Others (gay and straight) are quiet and some (there's that word again!) are extremely reserved. Of course you wouldn't notice these people but it doesn't mean they are not there.