How to switch my SGS3 to a 'google play' edition phone? My Samsung Galaxy S3 contract ends in few months. I'd like to get rid of unwanted stuffs like touchwiz,  flipboard, allsharecast, etc. and pull latest updates directly from 'google play', just like the rest of nexus phones.

Is rooting the only option available for me? Shouldn't Samsung allow me just point my phone update link (?) to whatever I want, as my contract expires?
Is rooting the only option available for me?


Yes.


  Shouldn't Samsung allow me just point my phone update link (?) to
  whatever I want, as my contract expires?


No.

The manufacturers do not have a legal or moral obligation to do so. They can provide the sources to the kernel on their site, that is about how far they can go.

This is where the community comes in, have a look at this titled "Where can I find stock or custom ROMs for my Android device?" 

Google Nexus line of devices are free from carrier related slow-downs in rolling out updates and fixes to Android, which is why you pay the odds over for a Google Nexus device.

Not all devices are deprived of the pure Google experience, i.e. no carrier bloatware, touchwiz, etc. It can be done by selected few talented developers, depending on the community and popularity of device in question.

You are free once the contract expires and do whatever you want without violating terms and conditions. 

You can:


SIM unlock/Network Unlock
root the device
modify it
flash a custom ROM on it (refer to the linky above)