Are there any data on how often this actually happens? This article from the British Medical Journal http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1499543/pdf/bmjc... suggests it has happened at least twice in recorded history. If that is representative, the real risk is presumably rather small.
That might have originated in seeing a cat sniffing a baby's exhaled breath. Much like a cat will sometimes sniff around your own mouth or nose, if its face is near yours.
I don't think the cat -killing- the baby is really a risk though. Though I would think (though with no authority... looong way from even thinking about having a kid) that when raising a baby, you want to reduce the number of variables to deal with. That cat messing around with your baby (maybe she'll make him cry a lot) seems to be one of those variables you'll try to eliminate and then introduce later whenever your kid is now at 'chase the cat and make her angry' stage or something.
http://www.amazon.com/Tattle-Tale-Sonic-Training-Alarm/dp/B0...
