Not clear from the article that the headline is accurate.
Lots of IT orgs would like a system that combines the common mail client with an integrated calendaring system, but mainly what we've seen for the past 15 years is crap "groupware" suites, Exchange/Outlook, Lotus Notes/Domino, Novell Groupwise, are/were the cream of the crop. Which is to say, what groupware is out there for enterprise IT consumption is basically dreck.
Domino is near universally reviled, Gorupwise would be, except it's never been that popular. And the (apparently) most common of the bunch, Exchange/Outlook (and it's Entourage client on Mac) has mail clients (Outlook/Entourage) that routinely masticate and ingest their own local message databases.
Not to mention the native Exchange client<->server comms protocol seems to be fairly chatty and inefficient. Experience indicates that Exchange also makes for a rather poor performing IMAP server as well.
Being a Mac user for the work machine, this is why I'm now fetching mail using spop with thunderbird, and only firing up Entourage when a meeting invite (*.ics) needs to be accepted and posted to the server side calendar. Which I read using OWA.
If the FOSS community ever comes up with a solution that can replace the common integrated mail/calendar solutions in use today, plus provides the bridge (eg. Cal/DAV support) to a non-Exchange solution, I predict that the rate of uptake would surprise lots of people.*
I don't think anyone ever cared for all the extended features that groupware offered, the users just wanted the calender integrated with the mail client and the meeting scheduler applications.
For most of us, any features beyond mail and calendaring are just useless dreck.
And it doesn't appear that Google has come anywhere near solving the problem described above. Because the cloud has nothing to do with what the users want.
*Maybe folks will post notes about non-MS mail clients that support Cal/DAV. Evolution is the only one I know of, and it's kind of iffy, depending on implementation. The version included Ubuntu 9.04 was the first one I've seen where the calendar interface to the Exchange server actually works.