Outlook works just fine talking to Google Mail; our Windows users connect to Outlook. The rest of us Mac folks use Sparrow (which is not long for this world, unfortunately).
Everyone has iPhones, which work great with Google Mail and Google Calendar. I'm exceptionally happy that, for most small and medium sized businesses, there's no need for anything other than Google Mail.
I'm not entirely sure why "Enterprises" would need Outlook, but I'll cede that's a market I don't know very well, so there may be very good reasons for it.