Blame the chemists
Sulfur is the correct, internationally-agreed spelling for element 16. To quote the mad-book:
'IUPAC adopted the spelling sulfur in 1990, as did the Royal Society of Chemistry Nomenclature Committee in 1992. The Qualifications and Curriculum Authority for England and Wales recommended its use in 2000, and it now appears in GCSE exams. The Oxford Dictionaries note that "In chemistry... the -f- spelling is now the standard form in all related words in the field in both British and US contexts"'
If it makes you happier, it's a one-all draw as the internationally agreed spelling for element 13 is 'aluminium'.