I agree, and when I worked in that world it was a huge pain in the ass. Users don't care about RFCs though, they just want the Internet to work, so you end up doing something that's pragmatic but kludgey. As I pointed out in another comment, Google is responding with a TCP MSS of 1430 (so assuming a PMTU of 1470). It's just what you do so you can get on with your business.