There have been quite a few topics on this over the years, though it seems the current consensus is for sites to adjust this as they see fit.
Interesting reading though:
Change to DD Mmm / Mmm 'YY for post dates
Displaying dates of posts - mixed formats make it hard to read
Year should be added to post date at some point
Year format on abbreviated post dates not clear
Add full year to date to make them less visually confusing