What I find interesting is that on the couple of dc14 standard ( with out brush control) that i have seen here, have the little release catch fitted to all dc07's , I have to wonder why this is.
One of the main reasons I can see of moving the filter from the side of the motor ( dc07 ) to inside the cyclone unit ( dc14) was that the filter could be bigger in size.
It is interesting to note that the new dc27's and 33's have there filter located on the side agian.
The cyclone on the dc14 makes the motor spin much faster than on the dc07 thus it works harder and fails faster
I do also think a bit of it is down to how the machine is looked after. I find that customers who have the dc07 tend to look after them more than customers of dc14's . they always come in bashed and smashed That is my opinion though