Most commericial web sites already deal with this issue - they have new/beta features that are initially only visible or available to a subset of users. Google Apps lets you choose if you want the new or old version... it's not impossible to let users stay with a static implementation, but it's just generally not worth the trouble.

Conversely, native apps suffer from the problem that once you deploy a package out the store, you have to support it (unupgraded) for the foreseeable future. That creates its own bucket of issues.