I mean - imagine Vista, or Win 7 going on the phone, just with a new touch UI framework added. It simply wouldn't work, couldn't work, would be impossible, beyond the reach of the richest software company in the world.
Sometimes, good engineering does pay off, and ultimately one could say that iOS is a direct result of good engineering. Every time the iOS wins it's a win for good design, and for object oriented programming.
That said, the dark side of being so far ahead of everyone for so long is a severe case of NIH syndrome at Apple. Those times when others surprisingly better Apple, Apple takes a very long time to catch up. Dev tools are the best example with XCode 10 years behind Eclipse. MobileMe Mail is perhaps another one: MobileMe Mail is similar to Mail.app on OS X - but Gmail is way better than that, and has been pretty much from the beginning.
Are you trying to imply that the base OS is bloated? Or, are you trying to imply that the UI frameworks are bloated?
Apple didn't just port Mac OS X to the iOS platform, they more accurately ported the underlying Darwin OS to it, and added UIKit and other specialized frameworks.
I think they were more concerned with preserving certain frameworks and their time-to-market given iOS & Android's market dominance.
Honestly, I don't have much confidence that Microsoft will get it right, in the long run.
I'm not a fan/foe of Microsoft, merely an observer, but I think their days of greatness are long past.
I must admit I've never seen this stated anywhere official, I just assumed it based on the fact that the minimum footprint for WES is 40MB, which was the same figure quoted for MinWin.
http://en.wikipedia.org/wiki/Minwin#Releases
An interesting excerpt (iirc, Eric demoed this in a Channel 9 video):
In October 2007, Eric Traut, a developer at Microsoft, demonstrated a self-contained MinWin system, made up of about 100 files, on which a basic HTTP server was running.[10][11] Traut noted that MinWin takes up about 25 MB on disk and has a working set (memory usage) of 40 MB. It lacked a graphical user interface and is interfaced using a full-screen command line interface. Traut explained during the demo that MinWin would not be offered as a stand-alone product, but would instead be used as the basis for future operating system releases such as Windows 7.