Eh, I never seem to know what's going on...
neither do we most of the time
Just to keep you in the loop...
http://en.wikipedia.org/wiki/Send_to_Coventry basically that's that old joke!
The extra screwdrivers = hammers.
Basically suggests the lack of intelligence of an areas tradesmen. Being a bit stupid and putting screws in with a hammer!
But all phrases are just commonly used by various tradesmen to ask for a (usually) "big" hammer to get something finally into place.

no real malice for the area mentioned

I usually ask for the "micro fine adjuster" myself. (meaning a very big hammer!) It kinda flows of the tongue better
But if I'd written that it wouldn't have had that same quick hit humour I was looking for!!
All that from a quick joke!!
I hope that's cleared it all up?
Ralph.