So would it have helped if Microsoft had been ingenious like Apple and called it Windows phone 8 but delivered fewer features instead to older devices?
No it would have helped if Microsoft had provided the WP8 update instead of just a UI tweak. Spiffing it up to look like WP8 solves only a cosmetic problem, it doesn't allow WP8 apps to run on older devices.
In a major update like WP8 or iOS 6, APIs are depreciated and new ones that are exclusive to the newer OS are introduced. Having everyone on the same version helps developers target much better.
If you think iOS 6 for the 3GS is just iOS 5 with UI tweaks applied, you're dead wrong. It's iOS 6 with features disabled so it will run better, not iOS 5 dressed up to look like iOS 6 which is what MS has chosen to do here.
