Yet if you'd read the info in the link, you'd see that even in the UK, appendixes was listed as a plural for appendix as far back as the 1800s.
Claims that it was always considered incorrect are simply our mistaken belief in an untruth.
I even remember learning that appendixes for the human part and appendices for the sections in the back of the book -- also apparently not based on any logic or truthful foundation.
Nonetheless, usage (eventually) determines correctness. If 99% of the educated people continue to rebel against appendixes, then eventually only appendices will be right.
http://www.richardbowen.com/appendix...ppendixes.html -- Well, according to the Oxford English dictionary BOTH appendices and appendixes can be used as the plural of appendix.