Control freaks
Don and Keith (who has a broken permalink) call me to task on my If you ever are in a position where you can control both ends of the wire... There are much better protocols than SOAP statement. This statement is merely a device I use to get to the heart of the issue quickly.
The primary purpose of this statement is to deflate arguments like this one. Read the entire thread to see how well it works.
It is also about setting expectations... for example: round tripping is not always 100%. There are a concessions one must make in order to achieve true platform and language neutrality.
But mostly it is to make the point that you rarely control both ends of the wire as much as you might think. Systems are fractal. Even if two relatively adjacent parts are developed in the same language on the same platform by the same company, if there are two teams involved and the interface is viewed as a contract, then it makes sense to view this interface as an fungible.