If you're talking about sheer data size you're wrong, since the GP's statement was regarding data storage.
If you're talking about individual bits of data, it's almost impossible to measure against eachother (unlesss both companies released figures). Facebook would host a lot of data in relation to messaging services but that alone brings up more problems in gauging the size and activity of Facebook. Every time I log on to my PC Gtalk and Skype runs the background. People who use Facebook occupy Facebook for prelonged periods because of how the service is devised. I'm almost certian that if it was a desktop app that ran in the task tray FB's page duration time would falter (right now my friend is using Facebook right next to me, she's having to sit on a website to "chat" to her family overseas, she'll log off Facebook and call them via Skype later in the day to have a conversation, a conversation that will cost her real money) *.
Consider, the average size of a WMV or MPG is far larger than wall posts and resized JPGs. Further, the Play Store (which is a part of YouTube) supports distribution of movies and music and does so to SmartTV's, SmartPhones, Gaming Consoles even most new BlueRay players sport a YouTube player of some sort.
* I do realise that Facebook is upping its game regarding these forms of services, the issue is that alot of it sits on 3rd party platfroms (like Skype), in actual fact a lot of Facebooks interactive services (such as Maps / Translations services) rely on the Microsoft.
P.S I wont even go into Facebook pages, many people may have them, many people may use them. I have now setup several of the things with paid adverising surrounding them, Google Adwords still drives more relvant and better customers to business sites. FB pages get likes, FB pages dont get $$ in peoples pockets and the latest figures show that nearly 2 / 3's of advertisers do not know how affective FB pages / FB advertising is for their companies - but this is another rant for another day.