That list is wrong. Although announced he would be the new manager Moyes didn't actually take over at Manchester United until July 1st so should be after Oscar. Same with Martinez at Everton.
http://en.wikipedia.org/wiki/List_of_English_Football_League_managers is a more accurate list. Oscar is...
Reports seem to indicate Wilder has now left Oxford and will join Northampton (Sky Sports News ticker confirms this too). Oscar moves up another place.
Moyes didn't take over as Man Utd manager until July 1st, after we'd appointed Oscar. He may have been announced as the new Man Utd manager but the list goes by when they started in the job.