One aspect that relates back to my earlier post, about whether the land needs protecting with RSPB reserves is still valid, if you look at national parks, a scheme that should protect the habitat in some way (may not be as good a s a full on reserve, but prevents mass development being carried out easily) and you will see the north, wales and south west are covered by large swathes where as the south east and east anglia are not.
http://www.nationalparks.gov.uk/map-homepage.gif
There may well also be better farming methods employed,I do not know this for a fact, but they don't get much worse than those used in Kent, for example in the Thanet area, farming is pretty much of cabbage, year on year, they plant them, harvest them, then scour the earth with acids and plant again, this has terrible affects on bird/insect life. If that is the case these areas again don't need as much protection.
It is also evident these days that small nature reserves alone are not as effective at encourageing wildlife as protected corridors or large areas of reserve, therefore the RSPB buying and maintaining vast tracts of land in one area is more important to wildlife than buying small areas dotted around the country. I'm from central England, and we have no RSP reserves nearby, yet our one reserve locally (at great Linford, the first inland site to hold breeding little egret) was offered for sale to the RSPB to help protect the area (which is under huge amounts of threat from development) yet they said no as they have enough water based reserves (or so I was told).
Alternatively maybe those of your from or in the Northwest just smell bad, and the RSPB want nothing to do with you 8-P