Re: wow
"Why?" you ask did MS have to move away from the Start Menu interface.
If MS stuck with mouse and keyboard and pen/touchscreen but better done under a revised Windows 7, then they would either have to
a) give up the tablet/big phone area of computing
or
b) have separate lines of O/S for those devices (as Apple have with their OS and iOS)
If a, then there's a chance that the tablet OS (Android, Linux, iOS, etc or something new) from competitors would break out of that area and invade the desktop borne on its small scale popularity. If b) you've got two lines to support which means more effort.
I don't think Win8 is the sacrifical lamb at this altar, so much that MS had to start somewhere. Perhaps they have bodged their attempt to deliver something that works for the 17 inch desktop in an office, a home cinema system, and a 10 inch tablet. To continue the OT theme, will God intervene at the last moment to save the first-born, time (as ever) will tell.