There is one ServletContext for an entire web application. This implies all the sevlets in that application has same one ServletContext. But here Session has nothing to do with ServletContext. What that statement means is " All the servlet that belongs to that ServletContext, would be able to access that session object, if any of those servlets are used for servicing that particular client whom that session belongs".
Neil - thanks for raising this one. I had the same query when reading the answer and thinking "but hang on - only if they are involved in the same session..." but didn't get round to posting anything here.
Thanks Kathy - I'll give myself a point for that question now - that brings me to 10/15 and some more reading to do!