My grandpa died last November 5, 2011. While I understand the disappointment, I wonder if I myself would play these shows if I were on their shoes. Additionally, canceling these tour shows is not good business, and would represent losses (plus really, how fair could it be for many other fans and the other bands?) Life is not always easy, nor convenient. Let them grieve their beloved grandma as they should.
You'll probably get more chances to liten to Anthrax in the future, as I don't see them retiring anytime soon.
And yes, Mr. Bello is as much Anthrax as is everybody else (my favorite band members are actually Frank and Joey, no offense to the other amazing guys!) He has a distinctive bass playing style for the band, not to mention his unsurpassed stage presence, backup vocals, etc. He honestly makes Anthrax as much as does Scott, Charlie, and the others, and I hope he plays along with Charlie on that last NYC show.