They are really missing the bus. A couple points stand out:
1) Microsoft needs device fanfare to accompany Windows 8.1
What, and 8.1 won't stand on its own? There has typically been two, maybe three primary reasons to upgrade Windows to a newer version (or replace the old) for 99% of everyone:
1) A new device is acquired and hardware support is lacking for the version you've already got
2) Planned obsolescence of software - you need the newer version of some program, which isn't available on the older version.
3) Corporate management benefits
Sorry, MS has never benefited from the "new shiney" Apple benefits from with every release of hardware. Their products have had to stand on their own merit. If a tablet comes out running Windows and is a success, it will be due to the benefit of any features of the OS more so than the tablet hardware itself.
the device would arrive in time not only for the holiday season, but also to cash in on user interest in Windows 8.1
There is user interest in Windows 8.1? This is news to me. Presumably this interest comes from the 5 people who bought Windows 8 laptops or desktops? Everyone, from corporations to home users, is trying brazenly to stay on Windows 7 or migrate from XP to Windows 7 (still, sadly), not to mention avoid Windows Server 2012 and the parasitic changes made to other Server 2012 products (Exchange 2012, here's lookin' at you, kid) which have overwhelmingly gimped their capabilities, management, and general functionality (though all reports of performance seem positive).
Regardless of why there isn't interest in 8.x, there simply isn't (just like Vista was/is hated, regardless of the merit of said hatred).
Surface devices released next year, meanwhile, could capitalize on enterprise hardware upgrades, which are expected to pick up as Windows XP's April 8, 2014 end-of-service date nears."
Companies will not be replacing their plain-jane XP desktops and laptops with Surface tablets, sorry. They're going to be buying plain-jane desktops and upgrading them to Windows 7, and sinking their teeth in for the long term (or simply upgrading the assets they have today). The software ecology is entirely too disruptive in 8 to allow for a clean "enterprise" migration - and the reliance on old versions of IE for corporate sites is still significant here.
I don't see Surface tablets succeeding if they a) ship with hard drives, or b) come with a price point more than 20% lower than capable but not-name-brand Android tablets: in terms of desirability, that's roughly where Surface sits. People have gmail, they use google for searching, and mostly watch youtube videos with their time. Surface isn't going there, in any regards - and most people don't have a Live account.