Web-based email usage down; Facebook and mobile to blame?

comScore's figures show that during November 2009 and November 2010, email usage has dropped significantly in those under the age of 54, with the Generation Z born after their older Generation Y siblings using email even less.
Surprisingly though, the Generation Y as the 'breakthrough' demographic use email roughly the same amount as their older Baby Boomer counterparts. Many would expect a smooth downwards trend the younger you get, but it seems those in their employment prime between the ages of 35-44 are exploring indirect alternatives to access standard web-based email.

Two things can be taken into account when reading these figures. It monitors web-mail usage, such as Hotmail, Yahoo! and Gmail, but may or may not take into account cloud-based email services like Google Apps for Education and Outlook Live provided by Microsoft's Live@edu. Also, mobile usage of email such as pushed email does not show up on this set of metrics.
In short, with a vast number of variables taken out of the equation, it could mean a couple of things.
- Web-based clients keep email directly in one place, but there is more reliance on mobile devices like BlackBerry's and iPhone's to keep email on the go.
- Facebook and instant messaging are on the rise in the younger generations, with more personal and pertinent information in news feeds giving context to the messages being sent backwards and forwards.
- Email isn't necessarily being used less, but perhaps the separation of lives is creating a distinction between work and personal lives.
What's your thoughts? Is email simply becoming 'less popular'?