EDIT: you guys have dug up some truly horrible pisstakes :D Thank you for those.
To the serious folk - relax a little. This is Mildly Infuriating, not I'm dying if this doesn't stop. As a non-native speaker I was taught a certain way to use the language. The rules were not written down by me, nor the teachers - it was done by the native folk. Peace!
It might have to do with grouping. Use less for one lump, use fewer for individual count.