The problem I see with this new "mid range" computer that people want Apple to build is the same I saw I saw when it was all about the "headless Mac": you want a lot of computing power and you want it for cheap. I don't blame you. I like cheap, too. Free is even better. Let's be realistic.
Several problems that get in the way of this:
1) Apple wants their stuff to be the best. They truly don't want to cut corners on design, outside and INSIDE of their computers. You want a mid range but Apple doesn't make junk. Their going to want the inside of their computer to look amazing. Sure you can buy a lot of computer elsewhere, but #1 you're running some form of MS OS on it. #2 it wouldn't look as nice on the outside (most likely) or as nice on the inside (definitely). Now for millions, this is no problem. For those of us running OS X, we know we'd never go back to Windows. Apple has no competition.
2) The PC world has cheaper computers because of competition. So they have to keep lowering their prices. But in lowering their prices due to competition, they're cutting corners in a million other ways. The overall QUALITY of the computer bought elsewhere will be less, every time. Apple doesn't have to lower their prices much because those who want OS X have to buy one of their computers to do so.
Recalling Apple history, the Mac7500/7600/8500/8600/9500 models had their CPUs on riser cards which made 3rd party aftermarkets very easy, which would have had an obvious impact on Apple sales because customers upgraded CPUs instead of bought new desktops...and even in those instances where the high end user move up, the still reasonably quick 180MHz 604e CPU card in his old 8500 could be popped into a 7500 to replace a 120MHz 601 CPU card, whch roughly doubled performance essentially for free...and without a dime going to Apple.
Agreed. Apple lets you upgrade your Mac Pro with other RAM/HD/Graphics cards because it's gotten at least $2299 out of you + probably another $1000-$1700 out of you for an Apple Display. Why allow the upgrade route for a cheaper computer, it's not making them any money. They don't have the marketshare to do what you're asking/wanting. They HAVE to have repeat customers. When they gain marketshare that's in the 30-40% range, you'll probably see your mid range computer.
Desktop Computers
Mac mini
599 - 1.83GHz Intel Core 2 Duo
799 - 2GHz Intel Core 2 Duo
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iMac
1199 - 2.4GHz Intel Core 2 Duo w/20"
1499 - 2.66GHz Intel Core 2 Duo w/20"
1799 - 2.8GHz Intel Core 2 Duo w/24"
2199 - 3.06GHz Intel Core 2 Duo w/24"
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Mac Pro
2299 - One 2.8GHZ Quad-Core Intel Xeon
2799 - Two 2.8GHZ Quad-Core Intel Xeon
3599 - Two 3.0GHZ Quad-Core Intel Xeon
4399 - Two 3.2GHZ Quad-Core Intel Xeon
I thought I'd take a look at all the price points for the Destop line-up. The biggest gap is the $400 gap between top tier Mac mini and the 20" iMac... but you're also getting more computer power, 130GB more HD space and a 20" built-in display. The $400 difference also comes in a quite delicious looking machine.
All-in-all, I think Apple hits all the price points it can while preserving its integrity to build the best computers. Are they always the most powerful or fastest? No. But overall, they perform wonderfully and they run OS X which, for most people, is the whole reason to buy from Apple in the first place.
Call it paying the Apple Tax. I prefer to call it getting what I pay for.