Are the built-in HTTP servers production quality?

[Paul Morrow]

I've heard it said that web servers built upon the standard library's 
SimpleHTTPServer or CGIHTTPServer aren't really suitable for use in a 
production system.  Is this still the case?  And if so, why?

Is it primarily a performance issue?  If so, aren't there a number of 
things that can easily be done to improve webserver performance --- 
caching proxy front-ends (e.g Apache's mod_proxy), faster hardware, 
server clusters, etc.?  Also it seems fairly straightforward to make 
them asynchronous (via the ForkingMixIn and ThreadingMixIn)...

Is it that they're not safe; can be easily compromised/cracked?  If so, 
wouldn't hiding them behind trusted front-ends (like Apache) help there 
too?

Are they simply too buggy to be relied upon?  They leak memory, don't 
correctly handle certain types of requests, or perhaps they're not 
standards compliant enough?

They're so easy to work with, I'd really love to understand what we 
believe their shortcomings to be.

Thanks.

Paul