Are you referring to the Bible? Because, unless you're under The Law -- e.g. circumcision, pork ban, etc. -- rather than under grace, I don't find a Biblical requirement for tithing.
Maybe that's all Kerry can give and still remain "cheerful."
Last time I looked, the average Protestant congregant in the US gave about 5%, the average Catholic 1%. Catholic congregations tend to be much larger, so they can support themselves on less. Also Catholicism is very top-down, Protestantism more bottom up, so people feel more connected to the Church.
I was raised Catholic and later attended a Protestant church. They asked me to join the stewardship committee in my first or second year. It blew my mind, here I was a relative new comer and I was one of three people directing finances. (BTW, the church mortgage was secured by liens on the homes of about 50 of the members.) I don't know of one lay person who ever even saw the books in my old Catholic parish.