Others have reported that the AMEX offer is still on other pages, I have not checked. The page I linked to was reported as not working (reported in another thread), and when I checked the AMEX offer had gone.

My theory, probably wrong, I suspect discussions went on late last night with AMEX (and failed) and the BA web team had to update the site asap today. The Welcome page was updated in haste, thus the typo, but the other pages have not yet been updated (or perhaps no longer accessible from the web site but from links in emails we received since end of December)? Alternatively, maybe was BAs idea of an April Fools!

EDIT: I did print a pdf copy of the web page