I don't think that Cassel has made $70MM in his career. His first4 years with the Pats were on his rookie deal, so he probably made about $2MM with them. His Chiefs deal was 6 years $63MM, which would have taken him through the end of the 2014 season, so even if he played that full deal out he would still be a bit under. But he didn't play the last two years under that deal, and made less money with the Vikings. The general point still stands though-he has made a mind-boggling amount of money in his career despite never being a top-tier guy.
With his new deal with the Bills I do think that he has signed contracts well in excess of $70MM in the aggregate, which may be what Rovell was trying to say.
It's hard to believe there's not a website that tracks lifetime contracts in football but I couldn't find one. At any rate, it's been Darren Rovell tweeting this (he started in 2012 by tweeting that Cassel had made $60m) but I agree with you that he's wrong.
Near as I can figure, Cassel made $1.5M with the Pats; $40.8M in his first 3 years with the Chiefs (remember he was franchised); in 2012, he had a base salary of $5.25M with workout bonus of $0.25M; then he made $3.7M in 2013; $5.75M in 2014; and will make $4.75M this year.
So at the end of his year, he will have made (if my math is correct, which it often isn't), approximately $62M.
I hope he has Bernard Pollard on his annual Christmas gift list.