Well, sure we are deep into implementation details, so it is reasonable for the implementation to treat stores to it specially. But the rest of the article goes

Well, sure we are deep into implementation details, so it is reasonable for the implementation to treat stores to it specially. But the rest of the article goes into details on how treating it specially causes "real pain in the neck" because the optimizer wants to optimize them away. It seems to me that if the store was not treated specially, the issue wouldn't exist in the first place. So either: exception handling in 32 bit mode is sort of an hack and the exception handling code generation doesn't actually expose the store the store through fs to the rest of the optimizer or, more likely, things are much much more complicated than described in the article.