So if I get you right, other than cost another reason for using generics is that the original drug is that the original drug has been field tested ( used for years by patients) and corrections, removal, or other modifications have been made to the original drug and have gone into the formulation of the generic. So if you need drug X and there is no generic... you get drug X. If you need drug Z and there is a generic of drug Z called GZ. If cost was not a factor, you would buy GZ because it would not have the problems associated with the present formulation of Z?
My assumption is that the original drug co. makes mods to improve the drug or application of the drug during the exclusivity period and this gets wrapped up into the generics. But I could be wrong on this.