If there's a direct correlation between the software and the OS it runs on, then yes, it makes perfect sense that--at least by default--some level of parity should be created in the UIs.
If there's not a direct correlation, then it's a bit trickier. If your app runs on iOS5 and iOS7, they really are entirely different visual styles, but it's one app, so it's a bit of a toss-up.
Some things to consider with iOS, however:
- Most iOS users are on the latest version at any given time. iOS users tend to upgrade more than other OSes. This chart shows iOS penetration by version. As you can see, as of Apr 3, 2013, 87% of users are on the latest full version, and 98% are on the latest or one back.
- The iOS has a very consistent/standard look and feel, but apps do not necessarily share it. Lots of apps veer wildly from any 'norm' and seem to function just fine.
So one conclusion from that is that it's probably not a bad idea to update your App to match the latest OS, since such a large majority of users will upgrade. Another conclusion is that if your App doesn't mimic the OS to begin with, it's probably not a big deal either way.