You've just pointed out that the general purpose CPU in the iPhone can run other software. This isn't what is at issue, what's at issue is the default/sanctioned install that comes with the iPhone. Of course you can get other android-like features on your iPhone if you replace or supplement the core iPhone software with something else. But then, your jailbroken iPhone isn't really an iPhone anymore, is it?
"Inspell" gives you red squiggly misspelling highlighting and intuitive spelling correction. It's a fantastic addition. Honest question - does the Android have something like this?
The default Android keyboard, and other keyboards, corrects as you type and/or gives you spelling suggestions and word completions. This has been a much better experience than having to go back and try to correct misspellings after the fact.