In the last 10 years Everton were at the top-6 five times, Aston Villa three times, Southampton once and Leicester once.
You missed Bolton in 2006-7. Also have to remember that in the last 10 years you have the nouveau riche Manchester City getting into the mix, basically meaning the usual 4 became the usual 5 and leaving only 1 team of unknown status being able to go into the top 6. And even this is up for grabs now days, as Tottenham have become a real force again along with Liverpool, basically cementing the "usual 6" yet again.
However if you look at the top 4 only.. then well a familiar picture is exposed. It is the same teams over and over again. Man U, Chealski, Arsenal, with Man City joining recently and Liverpool and Tottenham being a tad more consistent than most. Everton, Southhampton, Liecester .. all "one time wonders" basically and all because one of the listed teams screwed up. For example in 2011-12 Newcastle got in top 6-7.. why? Because Liverpool failed massively that year. Same with 2009-10, when Villa were in the top 6-7.
But as I said, the top 4 rarely changes with a "Leicester" type team. One can claim that one of the reasons that Leicester won last year, was because Chealski failed so badly, and the other teams had a bad year. Had they been even remotely at their best, then Leicester would not have stood a chance.
Every country has X number of teams competing for the title, and in most countries you can pretty early call out who is in the run for the title.. and yes that goes for the EPL. Man U are pretty much out of it and Tottenham are fading fast as they continue to throw away points in games they should have won. That leaves Arsenal, City, Liverpool and Chealski. Arsenal will do the usual March madness and get 3rd or 4th as usual, leaving Liverpool, Chealski and City. City are hot and cold at the moment (typical City one could say), and have European football as a priority I suspect. That means Liverpool and Chealski are going to have an advantage in the title race over City and well then it is a crap shoot.
We shall see. At the moment I think we are seeing the top 4 or 5 who will fight for the title and of those the top 3 are the most likely candidates for the title... only Liverpool being "unusual" based on the last 10 years, but hardly unusual based on their history.
One thing that is for sure.. Sunderland will go down, with Swansea.. 11 games in and they are already 5 points behind 18th spot.. Hell I could see West Ham going down as well the way they are playing..