Well, Apple's Mac division has sort of plateaued in many ways. If you look back at 1998-2004 there were radical changes to the product lines frequently including generational processor updates (G3, G4 and G5), major software updates (introduction of iMovie, iDVD, iPhoto, GarageBand, 10.1 Puma, 10.2 Jaguar, 10.3 Panther, 10.4 Tiger, etc) and complete design overhauls across the board.
Mac product design has been relatively the same since 2003/2004, Mac OS X and iLife development has slowed down considerably and Apple's been milking the Core 2 Duo line since 2006.
We've reached a point where Apple's Mac products (both hardware and software) are mature.
Just to grab something to debate - not taking sides but fun to play devil's advocate sometimes
Tiger 2005
Spotlight, Dashboard, Smart Folders, updated Mail program with Smart Mailboxes, QuickTime 7, Safari 2, Automator, VoiceOver, Core Image and Core Video.
Apple released the first Intel-based Macs
Leopard 2007
supported both PowerPC- and Intel x86-based Macs
Updated Finder, Time Machine, Spaces, Boot Camp pre-installed, full support for 64-bit applications (including graphical applications)
1st BSD-based OS to receive UNIX 03 certification.
Snow Leopard 2009
Microsoft Exchange Server support, new 64-bit technology, QuickTime X, advanced GPU performance with OpenCL, better use of multi-core processors through Grand Central, and SquirrelFish JavaScript interpreter
Mini tower isn't exactly new technology. It's a route Apple currently doesn't seem to want to take. Same with swap out HDDs for iMac - that's a internal redesign request.
Support for all off the shelf graphics cards? Not likely, though likely to increase for the Mac Pro only, more cards that can be added - the benefits of Apple pushing OpenCL.
Displays is a reasonable request - I hear they've thinking of changing the units to decades for the ACDs on the Buyer's Guide. LG should help out that one.