Really interesting idea and it would make a lot of sense. The reason why so many folks (myself included) had issues with their home buttons on the current iPhones is because of debris getting into the bottom of the phone via the dock connector. The type of connector you described above would certainly help to alleviate that issue.
Hah. I was given a second-hand iPhone 4 (to replace my old 3G whose dock socket had become blocked by some kind of debris in there), only to find the 4 had a dodgy Home button. I didn't realise that could be caused by the same socket issue.
I guess that's now 2 reasons to prefer a magnetic connector!