Is logoff feature necessary

[test.future () gmail com]

We have a web applicaiton which do not have logoff button. The developer claims that it is unnecessary, since the 
session can be terminated by closing the browser. Is it correct? Thanks.

-------------------------------------------------------------------------
Sponsored by: Watchfire

The Twelve Most Common Application-level Hack Attacks
Hackers continue to add billions to the cost of doing business online 
despite security executives' efforts to prevent malicious attacks. This 
whitepaper identifies the most common methods of attacks that we have seen, 
and outlines a guideline for developing secure web applications. 
Download this whitepaper today!

https://www.watchfire.com/securearea/whitepapers.aspx?id=701300000007t9r
--------------------------------------------------------------------------