Apple seems to really be trying to stratify their customer base, which is why the "Pro" model has more features and a significantly higher cost then the "non-Pro" model.
And Apple under Steve Jobs has fought very hard not to be "just another PC maker". When they released the original CRT iMac, all-in-one units were failures in the marketplace. And yet Apple turned it into a strong sales niche for them by doing it better then anyone else did. They took risks (USB? Nothing supports it! No floppy? How do I get my data on and off the machine?) and they made them pay off.
If Apple releases a mini-tower, it has to become the new iMac because sales of the integrated model will drop like a lead brick in a neutron star's gravity well. Nobody with even a basic education on the iMac and the "tMac" will buy the former and every website and Mac magazine is going to be providing that education.
This will force Apple to not only constantly update the ACDs to ensure they are feature-competitive with the competition, it will also force them to be very aggressive on price. The majority of consumers won't care about S-IPS or LED backlighting or such. If the cheaper third-party LCDs "look good", that is what they will buy.
And the "tMac" will likely savage Mac Pro sales, as well, as most folks discover they don't need the "Pro power" and take the cheaper "tMac". So the professional model might see even longer refresh-cycles because the lower sales volume means Apple has to keep shilling the same old stuff longer to earn their RoI. Which may cost it marketshare...
Whilst I agree with much of this and your later post, there's something to be said for maccompaq comment about being inside steve's head. I read many similar posts explaining how the fullscreen ipod would cannibilise iphone sales and damage apple's chances of achieving 1% market share, without any of the continued revenue stream that exclusive carrier deals brought with it. Nonetheless, the ipod touch was released and priced a flash generation ahead of the iphone so that the features the ipod touch lacked (mainly just the phone) were reflected in its retail price, regardless of the revenue stream the exclusivity with the carriers supplied (which is assumed to be particularly favourable for new contracts, ie switchers from other networks for whom the ipod touch provided a more capacious alternative.
whilst most of your points are spot on, i think its fair to say you overstate the damaging effect on overall mac revenue a tmac would have:
apple's desktop line has not been as successful as laptops in recent years. I'm pretty sure laptops are growing much faster than desktops at the moment (across the whole industry, but particularly with apple cos of the obvious gap in the desktop line).
Of the rivals you mention, only the imacs are believed to sell all that well. I would have said the mbp would suffer as much as the imacs anyways, as lots of ppl replace a midrange tower with a mbp +extra screen setup (up until this last imac update, the mbp was always as good as if not better than a 20-in imac at that time).
MPs may lose some sales, but lately apple has been very competitive on pricing vs dell with these, so they're probably not as profitable as they were pre-intel.
Most xMac'rs are completely unrealistic in their goals considering the prices they throw around ($999-1499). it doesn't have to be expandable, it just has to have discrete gfx. U can bet that if apple makes one, its margins won't be as thin as an equivalent dell the way the MPs are.
imacs will remain popular with students, women, anyone with space concerns or in need of an elegant lifestyle solution. The tmac meanwhile would sell much better than the imac currently does, meaning an increase in sales that would outweigh any loss in margins.
around 1 in 3 ppl would buy an apple display with the tmac, which would work out more expensive than an equivalent imac
tmac owners would upgrade much more often than imac owners do as they could keep the same display. personally, i'm a little resentful about how quickly my imac became obsolete and won't replace it for another year (its 4th) as it's doesn't seem very economical to. when i do i'll get the mbp + screen setup.
i wouldn't sell my tmacs off on ebay either, i'd put them to use in the living room (htpc) or give them to relatives who would otherwise never buy a computer (my mum)
Maybe my circumstances are unique, but apple would get a lot more of my money if the mini cost a lot more, had midrange discrete graphics and a 7200 rpm drive. but for all the fanbois who bash the xmac for potentially cannibilizing other mac sales (none of whom have ever offered the kind of eloquent and well thought-out argument that you have - no disrespect), there seem to be many more people saying they would buy them than not. I don't think it's such a leap to assume that that trend suggests the computer would be more popular outside the apple community than any other model. And there you have it, a new mac mini for the intel era, that costs more, has a greater profit margin and brings in switchers like no mac before it. I hardly think the shareholders would be braying for jobsy's blood.
i could go on and discuss what evidence suggests they won't be bringing out an xmac (24inch imac, return of the single processor mp, shift in focus away from macs at apple) vs the evidence they will (these persistent conflicting rumours about the mini, the loons who tried to profit from the osx86 project, the ongoing success of these mini-related threads), but i've waffled on for too long already. sorry about that.
tv, but the flexibility of a MM with FrontRow is mighty compelling.