The square shaped hero with the chin and buttons was released in the middle of the summer in Europe. It's a wildly popular phone. It is a GSM phone. Sprint decided to carry a CDMA version of the Hero and as most carriers do decided to make changes to the look of the phone. Verizons Droid Eris is another variant of the Hero and has a different look as well. This is pretty common stuff do some Google searches and compare each carriers version of the HTC Touch Pro and HTC Touch Pro 2.
Personally I like the look of both devices but prefer the GSM model, however I am not sure how much I would exactly like it if I had it in my pocket or hand. I believe Sprint did the redesign in an attempt to appeal to a wider population.