I believe that if a wifi connection is lost your phone automatically switches over to data. If one of those apps is constantly updating, and your wifi connection is a bit spotty (even the best wireless routers tend to disconnect occasionally) your phone may be switching over to data connection for a brief period.
(I don't know this for a fact, but Skype, for instance, may poll every ten minutes or so to check and see if you have any new messages... if you're not connected to a wifi hotspot, it's going to use data to do that)
There are many explanations, but that's just one. You may try disabling data on your phone or calling your carrier and telling them to disable all data connections.
