I notice that apps like whatsapp switch from loudspeaker to earpiece speaker if you hold the phone to your ear. It was so simple, I thought I had a weird bug where it would switch between the two, then I realized it works if I just hold it to my head. Perhaps this is the same for Skype or for the media player in general on the phone?
Windows Phone 8.1 will allow the user to explicitly pick the following:
Option to update store apps when only on Wi-Fi
The above is listed as a feature available in the Windows Phone 8.1 preview to developers.
The entire list is published here.
There's an article on the how-to section of the Windows Phone website, namely How can I minimize my data usage?. The article gives several tips and this one might be helpful to you:
Prevent cellular data usage when Wi-Fi connectivity is limited
If your phone is connected to a Wi-Fi network and can't complete a task because connectivity becomes limited, ...