It seems to me that if you adjusted your font size and icon size this would be quite usable.
Not really. If you scale just the fonts and icons, then your UI elements, bitmaps and any app-generated content measured in pixels will not be scaled. It will be hard to click on typical-sized objects, and UI layouts may also get messed up. (Go change the system font size on Windows to something large and see how many apps end up with their layouts mangled.)
The Retina mode, if it works the way Apple has been describing, does this right. The UI elements are scaled, and (I assume) legacy apps that do pixel-based drawings with the pre-retina APIs will get their output scaled to keep the proportions and layout correct.
I assume that apps using non-pixel-based APIs (e.g. vector graphics, and rendering bitmaps with embedded dpi information) will immediately benefit. You won't see a pixel-doubled 1440x900 but instead same-(physical)-size objects with more sharpness and clarity. (Assuming the source bitmaps have the resolution in them, of course.) And I assume (but could be wrong) there will be some new APIs to allow retina-aware apps to directly access the native resolution using pixel-based APIs, for those apps that require it.
Apple has been steering application developers away from pixel-based graphics for a long time. The introduction of retina displays on the iPhone and iPad have (hopefully) gotten them comfortable with the concept that using one on a Mac won't be a deal-breaker.
Seeing that this is possible I could never be content running at a setting that fits less on screen.
Once the typical font size and UI elements get too small to comfortably read/click, adding more pixels without scaling detracts from the user experience. You and I may disagree about what is "too small", but I hope we can agree that there is a limit here.
I don't think (for instance) that anybody would want to use (for example) this resolution on a 9" display without some degree of scaling.
Taking the discussion to external displays, I'd love to use 2880x1800 on a 24" display without any scaling - at that size, the UI elements will be big enough for me to comfortably use them. But I have coworkers who would hate it - they are currently running 24" displays at 1280x800, because they prefer their content to be larger. I'm sure they'd love some retina-like scaling on their displays (that have a native 1920x1200 resolution) if it was available.
Why is everyone obsessed with changing the resolution of the retina mbp? I prefer to see things the correct size...
What does "correct" size mean for a computer display?
Do you mean you want 12 point type to be exactly 1/6" tall, as it is in print? Do you mean you want an image made from a 1200dpi scan to render at 1" per 1200 pixels regardless of the display's native resolution?
This is exactly what the retina tech is supposed to deliver. Instead of rendering text and images at arbitrary sizes (e.g. assuming 1 pixel per point, or rendering bitmaps at one pixel per image pixel), these elements all have real-world sizes, which the system software will use to automatically determine an appropriate scaling factor when they are rendered.
Now, some people may want their UI elements to all be rendered at 1/4 scale on a retina display. That's fine. I'm hoping that some future version of the system software will offer a tuning utility where you can simply set a comfortable scale factor, and always leave the display's "resolution" fixed at its native res. People will be able to get the size they want, and the system will be able to use all the available pixels to render the output as sharp as possible.