Originally Posted by SolipsismX
You can't compare Macs to iOS-based iDevices because the logistics are completely different. You can hook any size monitor up to a Mac. Apple starts at 11" and while that gets quite small and many pro apps simply aren't designed with that mine for general use it works out and there are certainly advantages for the small size device. Or you can go to 100" HD projector if you wish, not using an Apple display at all. You can use any
aspect ratio that suits your needs.
You simply don't have all those options with a non-windowed OS without a direct and severe hit to the user experience. For those reasons I think the most likely avenue for Apple to increase the display size to keep the PPI the same and increase the resolution on one or more axis. This allows for any current iPhone content to be displayed on a larger iPhone exactly, pixel-for-pixel, the same size today as it will tomorrow. Devs will still get a new SDK and updated apps will be the better for it, just like with the iPhone 3GS to iPhone 4 transition.
FTR I wasn't comparing devices as much as markets. I believe the cell market's roughly a billion units per year - and the new tab market is roughly a tenth that (with likely half or more of those Wi-Fi devices). Apple's disrupted and transformed the former one device at a time - by revealing that what were being thought of as smart phones were really pretty dumb, and they've jump started and validated the latter - again by showing no one else had grabbed the metaphor for what a useful/user friendly tablet could be.
But now that everyone and their cousin in the industry is focused on mobile computing - and now that consumers begin to see all the possibilities, going forward I don't expect Apple to try and fill every niche use with a plethora of specialty mobile products, but I do think it will take more than one "phone factor" device and one "tablet factor" offering to cover even the mass markets and leading edges of where the mass markets will be going as the tech and engineering drive relentlessly forward.
My signature example for a future not-so-sy fy iDevice is a 20"+ flexible sheet that rolls up into a cylinder - with application for consumers (reading the paper on a commute, collaborative gaming on the device or across the net, a portable multi-person HD movie experience anywhere, anytime, etc., etc.), for business - instant design and markup collaboration, presentations and conferences anywhere, blueprints on the 80th story - with the ability to change 'em on the construction site, again, etc. ad infinitum), and for the military (obvious applications all over the field).
Meanwhile, Apple's got this Other Line that no one talks about much anymore - the iPod (since anyone with a smart phone or iPad already has their music on their phone or pad - which is very successful in gaming, but kind of superfluous strategically at the moment. This is one place one could see some tweener sizes for dedicated devices that don't need phone service or which can rely on Skype type services.
Apple (along with Android and some interesting work at Nokia) has already knocked a good amount of the stuffing out of point and shoot cameras with only what they can cram into an iPhone (along with the phone and computer).
I think a 4-5" iPod class device optimized for photography (real zoom, better optics (even if the optical path has to turn and do other tricks to keep a thin device that's also a good reader/gamer/semi-pocketable) and useable amounts of flash or video light, e.g.) - and still a potent (more potent) game device - and able to run all those other apps, and be useful with video and book content - and if marketed liked a tablet class device with, say, LTE as an option (but not called an iPad) - could grab another nice chunk from all the camera makers - and further blunt any market share progress by Android or MS. And no one's really done this yet. I.e., could be 10M+/yr device market between say $299 and $499.
The cam makers are starting to add Wi-Fi and other iDevice features - but a Coolpix that can transmit pics/vids on a home network or even post them to say, facebook or YouTube, is not an iPhone or an iPad. It's a camera with a few extra tricks - and couldn't hold a candle to an Apple device, even if marginally better as a shooter. And again, that's just an existing market. There are more brand new ones to come. As Apple has proven repeatedly with the three devices discussed here.
Also, as iOS and its processor families develop (tho' tech-knowledge-wise I realize I'm just talking out of my butt here), more of the screen management chores could (as I think I kind of understand) be abstracted into to the OS - making more screen sizes and even aspect ratios far less painful for developers. Or maybe not.
But my point is that while you're right about the current market - where brilliant engineering has won amazing share with only one new basic phone and tablet model per year (or less!) - both of which have turned out to have totally hit the sweet spot for compromise between all the mainstream uses to date as highly adaptable general use devices - we haven't seen every class, size and form factor with enough market potential for Apple to target in this new world yet.