So I saw Mike's Open Letter to Steve Jobs and I kind of wanted to comment. Since he doesn't have a comment section...
First, from his letter, this one jumped out at me:
I rely on dual monitors and a Mac Pro is not within my company's or personal budget.
So here's a crazy idea, Mike: Buy an iMac.
From Apple's iMac page on graphics:
[...] all three iMac models let you use a second display in extended desktop mode -- in addition to simply mirroring the first.
So you can buy a $999 iMac and still use your second display with it. Or, if you prefer the beefier graphics cards of the higher end models, go with them. You can still use your second display with it.
On a more general note, though, supporting PCI cards actually requires some things such as a minimum size and all to keep things cool. Some of us old timers remember, for example, when IBM came out with the PS/2 Model 30 which would accept IBM AT cards--except that the enclosure was too small for them to fit. Apple's PowerMac Cube was another example--you could use whatever PCI cards you wanted, except that they had to be specially designed to deal with the Cube's size. Needless to say, I think only nVidia did one.
So, in other words, you want a Mac in PC clothing.
This isn't a bad thing to want. Personally, I sort of agree with you--I'd like to see Apple do an inexpensive Core 2 Duo tower. But I recognize that my aims and Apple's don't mix.
First, I think you overestimate the market for this. The "Tech Savvy" market is nowhere near as big as we geeks tend to assume. There are far more people who will be wowed by Mac mini's small size or the iMac's stunning looks than would be interested in a "Me too" looking tower. For business who want dual-monitor support as inexpensively as possible, again, the $999 iMac rears it's head. For home users wanting to replace that virus-ridden desktop, the Mac mini and the iMac will fill their needs quite nicely. The lack of expandability isn't really hurting Apple. Macs are expandable "where it counts"--memory and hard disk space.