In Windows 8.1 Preview this had finally been updated to PowerShell, but it appears that in the RTM version it's been made an option:
In the task bar properties dialog in Windows 8.1 there is a new tab "Navigation" which has on it a checkbox: "Replace Command Prompt with Windows PowerShell in the menu when I right-click the lower-left corner or press Windows key+X"
I don't know why, in a new OS (with a brand new menu), Command was ever placed on that menu, but now that we've got PowerShell there -- you should not regress back to Command. I suppose that somewhere there's someone that still wants to launch the command prompt instead of PowerShell -- but that's obviously the OLD way of doing things, and it shouldn't be the default.
PS: why does that say "Windows key+X" instead of "Win+X" which is what everyone knows?