This whole thing doesn't really make much sense to me. I was at Best Buy yesterday checking out the 27" iMac and the fonts/UI items didn't really look much larger than what I see on my 13" MBP.
Your 13″ MacBook Pro has a 1280×800 resolution, which gives it a pixel density of 114 PPI.
A 27″ iMac has a resolution of 2560×1440, which gives it a pixel density of 109 PPI.
This means that everything will be rendered at roughly the same size on both displays, but due to the higher resolution of the 27″ display, you will have significantly more workspace.
If you're gonna give me the option to plug my 13" laptop into a 26" external monitor (twice the size of the laptop screen), shouldn't you assume that maybe I'd like the option to double the size of everything on the display?
Actually, if you enable HiDPI mode on Lion/Mountain Lion, you will get exactly that.
If you simply want more screen real estate, you already have the option of using multiple monitors. But if you just want to double the physical size of items being displayed, it's not really do-able (at least not with the options that I've tried).
Multiple monitors are a terrible solution. For one thing, OS X does not have very good support for them. Your dock and menu bar only appear on the primary display (or in some setups, on
separate displays!) and there have been numerous studies that have shown it to be considerably more efficient to work on one large monitor than have several smaller ones. The second display is less functional, and ends up being neglected, or used to display relatively static information such as leaving an email client or iTunes open, rather than actually making use of it for work.
That said, with Lion/Mountain Lion, you can enable HiDPI mode, which will render everything on-screen at 2× scale. This maintains perfect sharpness, but makes everything much larger.
With most current Macs, it is not feasible to use this option though. A 1280×800 MacBook Pro would only have an equivalent workspace of 640×400, which is sub-VGA resolution.
A 27″ iMac is where it starts to become a realistic option, however. At that resolution, your 2560×1440 display now has a 1280×720 equivalent workspace, which is enough to actually be productive.
As higher density displays are introduced, this becomes less of a problem. At 220 PPI, the Retina MacBook Pro has a high enough pixel density, that non-integer scaling becomes feasible without severely compromising image quality, which is why it offers more than just 1× or 2× scalingit offers equivalents to 1024×768 and 1280×800 for people that wish to make the UI larger, and 1680×1050 or 1920×1200 for people that wish to make the UI smaller, all while maintaining a sharp image.
And why does lowering the resolution only center the picture inside of the display? That makes no sense to me. If I lower the resolution on my PC, I still have a full screen to work with. On the Mac, I lose about 1.5" on either side of the picture.
Unlike CRTs which were analogue displays that actually scanned the image with an electron beam at the resolution you select, flat panels are fixed-pixel devices. This means that they only have one resolution they can display images at.
With a CRT, when you changed the resolution option it actually changed the resolution of the image being displayed.
With flat panels, when you change the resolution, you are still displaying the image at its native resolution, but have to scale up the picture, which makes it blurry and generally looks crap. If you choose to avoid scaling the image, it will retain its sharpness, but will no longer fill the screen.
