Can you mention even one?Actually, it does change.
Silver is just an element (or chemical if its not pure). An organism can build up an immunity like anything else.
Now some elements (Chlorine, Fluorine, Arsenic) are very hard to build up an immunity to mind you...
http://www.colloidal-silver.com/article2.htm
(in part)
In the 1920's, 30's and 40's, silver was ground very fine like flour, suspended in water and was used orally for many infections and disease conditions, topically on burns, and for fungal infections. Over 650 bacteria, virus, and fungi were considered treatable with this silver in 1938. With the development of the patented antibiotics, silver was forgotten in the United States and most other places, although the antibiotics are only effective against bacteria, not viruses, yeast, or fungi, as is silver. Now, with the greatly improved modern colloids, the tables are turning and silver may be the most effective treatment. The 1994 issue of Newsweek featured a six page article, "Antibiotics, The end of Miracle Drugs?" as the cover story. "The rise of drug-resistant germs is unparalleled in recorded history," according to the article. "Penicillin and tetracycline lost their power over staph back in the 1950's and 60's. Another antibiotic, methicillin, provided a backup for a while, but methicillin-resistant staph is now common in hospitals and nursing homes worldwide...Trying to cripple bacteria's defenses...will not do much more than buy us five to ten years... A better strategy might be to abandon antibiotics altogether in favor of different kinds of drugs." Not a very pretty picture.
The September, 1995 issue of Time Magazine featured an article titled "Revenge of the Killer Microbes." Sounds like a science fiction thriller, doesn't it? But Time was serious. "Faced with AIDS, and with an ever increasing number of antibiotic-resistant bacteria, doctors were forced to admit that the medical profession was actually retreating in the battle against germs. The question ceased to be, 'When will infectious disease be wiped out?' and became 'Where will the next deadly new plague appear?'...Humanity once had the hubris to think it could control or even conquer all these microbes. But anyone who reads today's headlines knows how vain that hope turned out to be. New scourges are emerging -- AIDS is not the only one -- and older diseases like tuberculosis are rapidly evolving into forms that are resistant to antibiotics,...In 1992, 13,300 hospital patients died of infections that resisted every drug doctors tried."
In the case of colloidal silver, the best you can get is what you make yourself so why would anybody go out and purchase something that, once you spend a whole $20, you can make several hundred gallons of it. (once you buy the distilled water which is about $2/4ltrs where I live and that amount should last you about a year) I'm quite sure you could buy some on-line for $20/oz that probably has no silver in it, it also degrades quickly if exposed to any light other than amber so freshness is a factorEdit:
Oh, and your kidding yourself if there isn't profit involved in these other safer* treatments.
* Im not sure what treatment you are referring to, so it may or may not be safer.