I wouldn't even say that. In most cases I'd say it's all about familiarity - both OS and application.
Perhaps a project manager needs MS Project, or an architect needs AutoCad or something but for the "teenage girl" demographic you would be hard pressed to find any particular application they absolutely needed that doesn't exist on Linux, or there isn't a ready counterpart (eg Adium instead of MSN Messenger). They're just not used to it and dislike anything unfamiliar, since computers are basically mystic black boxes anyway.
I think for many typical users it's simply a matter of preferring something they (mostly) know how to use.
It's important to use would instead of could when thinking about these things. If the teenage girl doesn't know about Adium, it's the same no Adium.
It's now more likely that she would Google "MSN for linux" and be successful. That's relatively new. It still leaves her less likely to having the messenger. That likelihood is not 0. Not even on windows. There are plenty of 14 year old girls out there that don't have MSN Messenger on Windows even though they 'couldn't' overcome some sort of hurdle.
Perhaps a project manager needs MS Project, or an architect needs AutoCad or something but for the "teenage girl" demographic you would be hard pressed to find any particular application they absolutely needed that doesn't exist on Linux, or there isn't a ready counterpart (eg Adium instead of MSN Messenger). They're just not used to it and dislike anything unfamiliar, since computers are basically mystic black boxes anyway.
I think for many typical users it's simply a matter of preferring something they (mostly) know how to use.