Personally, I'd be willing to give up instant access to my Michael Jackson catalogue (that is if I had it -- sorry, not a big fan of MJ) to be able to do GPS anytime, anyplace. I have all the songs I care to listen to on my iPhone, almost all of my 11 screens are filled with apps, and I still have enough space left on my measly 16GB unit to load maps of US, Canada, and half of Europe.
What you may personally be willing to give up, or pay for, is not much of a factor in a mass-market device. The manufacturer has to decide what the market wants in general in order to design and sell profitable devices. Selling cellphones jammed full of map data for any possible market the user might want to go would be of interest to a small number of people - including you - but not a profitable enough number.
That's why after-market applications are available, so that those who want something specific can find a solution that fits their needs, and not require everyone else to have to pay too.