Well of course to some degree that is true. Everyone's sweat is going to be salty but some will be more salty and some will be less salty. I have no data to back it up, but I don't think it would be going too far out on a limb to say that it probably follows some kind of normal distribution...

I am very much not a salty or high volume sweater. Therefore I drink less than many others and tend to avoid things with added sodium. If I take in too much sodium (and I mean even as little as what is in most sports drinks) I will retain water like crazy and feel extrememly bloated and uncomfortable. If it is very hot, such as 100F I will go through a bottle an hour but in most typical riding temps I'm more like 1/3 to 1/2 bottle per hour.