Why does clearing cache leave some cache files?

[parabellum7 at yahoo.com]

I've made similar observations in FireFox. I'm pretty confident I have it configured to clear everything, yet much remains ...

I also notice in Synaptic I can mark an application for complete removal and still find folders and configuration files all over the system. I was under the impression that one of the advantages of exclusively using Synaptic to handle applications is that fragments of uninstalled apps would NOT be left on the system as it is on that 'Other' OS.  ;]  

I'm not a developer so I don't know what technical reasons exist as to why delete cannot mean delete. 

Bleachbit, with careful selection of options, helps with cleanup. So, my fellow penguinites, what are your thoughts on using bleachbit? Do you use other tools or techniques to accomplish a similar goal?


-K