I find the uprights keep the filters cleaner than the cylinders. I reckon it's due to the size. An upright's cyclone is taller, so more chance of the fine dirt getting up high enough to work through the system is lower (still happens though). On a cylinder, cos the whole thing is shorter more dirt works its way through the bazillion mph downforce or whatever they call it today, and onto the filter!
There's probably a reason the early machines said to wash the filter every 6 months, then the newer ones say wash every month. Now they have no filters, and I'm skeptical about the whole thing!
What sort of dust do you have too? Fine light dust is always a pain, take plaster dust as an example. Sand seems to work its way out as well, the amount of DC07/14s I've had that have half a beach under the post motor filter is shocking!