Jonn Elledge writes
It's so damn obvious that if you cant work it out, you must be a bit
thick.

Patronizing tone aside,

I make no apologies for patronising people who have previously been
patronising towards me and who are also brainless idiots.

am I correct in thinking that you're referring to the levels of usage?
Fenchurch Street has approximately one arrival and one departure every
ten minutes, meaning that each escalator is carrying the passengers for
approximately six trains every hour. A station like Tottenham Court
Road, in comparison, will be catering for more like forty trains every
hour - which are, I suspect, longer, and certainly more heavily used
than the C2C trains.

So the wear and tear experienced by escalators at key LUL stations is
going to be a hell of a lot greater than that at Fenchurch Street.

They're also a lot longer.

Those reasons and more. One major reason being the location.

It's easy to forget that they are deep underground, which is not the
most easily-accessible place. Especially when it comes to replacing a
huge solidly-built escalator th at has been in situ since the 1930s.

http://tube.tfl.gov.uk/content/faq/escexplain.asp

or if you have time to spare;
http://www.lrb.co.uk/v24/n05/camp01_.html

--
Dave