There is ZERO lock-in with this service. If people want to continue to do hand code reviews themselves, they can. There is also ZERO in Amazon's announcement that implies this is just about improving code specific to Amazon's platform.
Stop being open source purists and start understanding reality. Many (most?) of the posters about this topic critiquing Amazon live in open source unicorn land, and seem to have almost no understanding of business realities. (Sorry for not saying what I really think but I thought I should be polite.)