The reason Apple have refrained from a typical computer without a monitor is that it would not be financially profitable.
Apple charge a premium on each product, and, deliberate or not, there is a hidden feature (or factor) within each product that silently justifies the price. Although you may think it is Mac OS X, it is not
For the Mac Mini, it is the form factor.
For the iMac, it is the 'all in one' factor.
And for the Mac Pro, it is the sheer power and expandability factor (and the 'look at me, I got a Mac Pro')
If Apple were to produce a basic tower, with only upgradeable parts, it wouldn't take people long to tot up the $ total of all parts and say "Hey, Apple is essentially charging $500 for Mac OS X" on this computer.
Apple wants you to buy the iMac as an average consumer (and tbh, it is a great computer for average consumers). The Mac Mini is to persuade those already with a set up not to say no because they already spent $$$ on accessories, and the Mac Pro really is for professionals.
What I believe you all really want is the form factor of the mini with the power of the iMac and the upgradeability of the Mac Pro. Sorry, but
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knows this would kill sales of all its current range of desktop computers.
As it stands, everyone puts up with the situation and buys what they can afford. For what reason would Apple's accountants recommend diversification? To please 0.2% of Mac users? It would be a pretty crazy fiscal policy
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