I think the difference is Old Yeller died a tragic,untimely death in a tragic way. Marley was very old,he had lived a long,full life,and it was time for him to ease away peacefully,and with dignity,which he did. It will be interesting to see how they do the final scenes. John Grogan,the author,had full creative control,I am sure he will let his beloved Marley go peacfully,and tastefully,on the big screen.And everyone,please read the book before you see the movie,trust me on that.