They'll still have to rewrite. The "infrastructure" he was referring to was GoogleFS/BigTable/MapReduce and their other massively-distributed backends. You don't have access to them if you aren't Google.
I've heard that GWT isn't actually used by any notable (= public has heard of it) Google project. Could be wrong though; no inside information.
I've heard that GWT isn't actually used by any notable (= public has heard of it) Google project. Could be wrong though; no inside information.