The problem is Skype recently moved to a centralized infrastructure instead of a P2P which has caused terrible issues for pretty much everybody. Allegedly this was done to allow the NSA to snoop on conversations easier.
P2P infrastructure isn't realistic when most of your clients are on mobile. Skype used to drain your battery simply by logging in for an hour. Now it doesn't!
Skype and G+ use the same codec families as well, so the differences would be in bandwidth allocation.
The battery drain could be from anything. I'm not sure if they use GCM (Google Cloud Messaging) to reduce battery these days but without looking at the code I don't think you could say switching to a centralised server model fixed the battery issues.
P2P infrastructure isn't realistic when most of your clients are on mobile. Skype used to drain your battery simply by logging in for an hour. Now it doesn't!
Skype and G+ use the same codec families as well, so the differences would be in bandwidth allocation.