Restrictive in the sense that the company now has so many devices out in the market that making more radical changes in the software (in this case the operating

Restrictive in the sense that the company now has so many devices out in the market that making more radical changes in the software (in this case the operating system) or by introducing not backward-compatible new hardware can affect millions of users with older hardware negatively. Apple still wants to support all the older iPhones so that they can get money from the app store, if an app would need to have a separate version for older devices it would change their app market in a negative way.