Um, it's not a theory--it really works most (>90%) of the time. The gallbladder is generally the site of the chronic salmonella infection that couldn't be treated before antibiotics.
Now, whether you want to have surgery back in a time before antibiotics is an independent problem.
Typhoid had a lot of attention because it tended to be one of those things that killed a LOT of soldiers. The vaccine for it was developed in 1896 by the Almroth Edward Wright at the British Army Medical School. And the Second Boer War was the first time that war casualties were actually larger than disease casualties because of the vaccine.
"In fact, the most widely accepted treatment of chronic typhoid infection is removal of the gallbladder."
And, in particular, it looks like the most chronic and asymptomatic (like Typhoid Mary) have biofilms on gallstones that serves as a very difficult to kill reservoir.