Of course Mario has been in more games than any other character in history. No person will argue otherwise. Well, actually, I've seen people argue otherwise, and they need to STFU.
And of course the Mario name helps the games sell.
Starting with Mario Kart, people started to expect a certain type of gameplay from Mario games... The sports titles, then the party titles... And Nintendo largely delivered that type of gameplay consistently. Other than the yearly Party iterations, they still protect their star by only doing sequels once per generation. Paper Mario, Mario and Luigi, Mario Tennis, Mario Golf, Mario Kart, and the rest have only appeared once each gen so far, and have never really been low quality titles. And so they've managed to avoid wearing out consumers on the brand. And when they do something new like Mario Strikers (or whatever), consumers still trust the brand more than they would "We Love Soccer" (or whatever).
I'm not sure there's really any "blame" at all. Mario games sell. The developer (rarely Nintendo), the publisher (Nintendo), the whole distribution chain, and the consumers are all a part of making them sell. And that's just a fact; it isn't necesarily a bad thing. The games are what they are and people shouldn't lament it.
Nearly 100 million games sold over the last two generations alone is obviously a winning strategy.
"[Our former customers] are unable to find software which they WANT to play."
"The way to solve this problem lies in how to communicate what kind of games [they CAN play]."
Satoru Iwata, Nintendo President. Only slightly paraphrased.
