In a post to the Outlook blog on September 12, Microsoft execs provided more as to why they added IMAP alongside Microsoft's own Exchange ActiveSync (EAS) protocol support. For those devices that still haven't (and may never) support EAS, there's now IMAP.
From that post:
"Outlook.com already supports the industry's best email connectivity with Exchange ActiveSync (EAS), which is available on the majority of smartphones and tablets, including Windows Phone, iOS, and Android devices, as well as the Windows 8 Mail app and Outlook 2013. With today's announcement, we now have a richer email experience across devices and apps, including those not using EAS, such as Mac Mail and Thunderbird on a Mac."
TripIt, Sift, Slice, motley*bunch, Unroll.me, OtherInbox, and Context.IO are rolling out updates today that integrate with the new IMAP support in Outlook.com. Microsoft is expecting other new ISV-developed integrations to follow.