iTunes shows many of my apps with "Update" but when I synch nothing happens
The iPod you are using (presumably the iPod 4) is no longer taken into consideration when new apps are being developed, nor is the operating system on it as both of these are obselete. This is the reason nothing happens when you sync your iPod. However iTunes just thinks that an app you are using is out of date and should be updated, without considering the device attached. So there is probably no way to single out the incompatible updates.

Hope I helped!