> If I am right about this, why do Americans, in particular make such
> mistakes?
Oh, it is not "Americans in particular". Apart from this list and my occasional contacts with home, I have had little exposure to American speech for the past several years, and I still find grammatical transgressions to tear my hair out about every day. My co-workers (all of them Irish), for example, are currently afraid to use either "imply" or "infer" because - for reasons that thoroughly baffle me - they can't work out the difference between the two, and know I will scream if they get it wrong *again*.
I'm hoping somebody will get me this for Christmas: http://www.thethingsiwant.com/reserve/pframeset.php4?ITID=283778&action=B