I found the following blog post which looks at how several of the apt related tools function together. It is interesting, well it is to me, and many Debian and Ubuntu users do not realise that the aptitude and apt-get are actually separate tools, and aptitude does not just call apt-get under the covers.
Anyway: A diagram of the apt system
Worth a read in my opinion
Thanks for that. I, too, misunderstood that. Good link.