Well, the original source is one of the most reliable types of sources you can get from Brazil (Folha de Sao Paulo is one of the most respected newspapers there), so I'm not concerned about the source not being credible. And about the translation, well, it's nearly impossible to give any other meaning to that quote. If you speak more than one language you understand the types of translation errors that can happen, and I can tell you that there's not a lot of ways you can mess up the sentence "advertisement generated was immense". You can translate it 100 times back and forth and you still won't get a 'his death made the sport safer'.
But the placement and wording in his sentences would have had an effect on how he meant it, yes? I'd like to see the full interview before jumping on his back.
For example:
"After Senna's death, safety was improved immensely, not to mention the advertisement generated was immense"
"Admittedly, the advertisement generated was immense but more importantly safety was improved after Senna's death".
The media are very good at dicing sentences to make them sound worse than they are. Just as much as translation can sometimes bring across the wrong impression, especially with a language like English which places a lot of emphasis on context and is also usually quite backwards compared to other languages.
Bernie has said stupid things before (e.g. Women in racing, Hitler comments, etc). So I wouldn't be surprised if he has said this, especially at the same time as the Brazilian GP, when it would create a media frenzy. But, I also see it isn't mentioned anywhere from my usual sources for credible news reporting.
People asking for Bernie to leave should perhaps think about what happens when that does indeed happen. Does anyone have a suitable suggestion for a replacement? Like him or hate him, Bernie does certainly sort things out and people are quite afraid of him. He has awful ideas and says stupid things, but I think he's done that nearly all his life. I seem to remember a certain quote from his Brabham days being quite apt, he was mad back then too.
When Bernie leaves, there will be a rather large grab for power and I'm not sure F1 will be better for it.