Not enough managers getting sacked?

Ok so I have just finished the first season in the prem for the 2nd time (first with Liverpool and secondly with West Ham) and in both theese first seasons not one premier league manager was sacked! Aston Villa at 16th...sorry but even Randy Lerner would lose patience with that...Portsmouth relegated...Hart wouldn't survive...Hull 19th, no way Phil Brown is still there. Even Fulham 14th would have a case although I think it's less likely Hodgson would be gone from that position. I could accept a couple of theese, but for no manager in the premiership to be sacked in a season seems a bit off too me. Are the chairman too patient?