Forrest- you will be on iOS5 within weeks after the software is released. (not to be confused with the iPhone 5- this is in regard to the operating system)
Apple makes it damn near impossible to avoid upgrading the software on your iPhone 1, 2, 3, 4, whatever...
In regard to Phone Guard- timing is key in this- why develop software for a operating system that will be outdated in a month when you can develop it for the newer version and use this as a catalyst for deeper promotions.
The product isn't out yet but developers likely all have the beta version of iOS5 already.