[WikiEN-l] Simple vandalism being missed

[Carcharoth]

I was recently looking up which countries were in the Congo Basin, and
the version of the article I found was this:

http://en.wikipedia.org/w/index.php?title=Congo_Basin&oldid=359085351

The list of countries is clearly missing.

It was removed with this edit:

http://en.wikipedia.org/w/index.php?title=Congo_Basin&diff=357222409&oldid=353051579

That was 20 April 2010 (I've now restored the list).

Has anyone done a recent study to see how and why vandalism like that
is missed and how common it is for such things to be missed?

Carcharoth