The reason Mario has remained so long is because you can almost always expect a quality game (a few exceptions). He is also appealing to kids and adults. It is a win-win situation. I do think Nintendo needs some new ips though. Project Hammer and US version of Disaster day of crisis, where art thou.
"Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth." -My good friend Mark Aurelius