the ultrabook comparable device would be the windows 8 based device with intel Ivy Bridge processors i believe. so you are talking a device comparable to the high end laptop devices. as for the launch window... windows 8 is not ready for launch right?
i guess the idea behind the event yesterday was to get developers excited for metro apps. i mean until now the reaction to windows 8 has been very mixed. there were too many doubts about the RT edition of Windows. microsoft has now clearly stated their intentions. they are serious about tablet pcs running winrt and developers now have real incentive to work on the apps for this platform.even if they could launch it today, it would not have worked well. simply because of the lack of apps. windows 8 consumer preview means that people have a working copy of windows 8 with metro in their hands. developers have the tools to create metro apps. microsoft is playing it right to ensure that there are going to be plenty of metro apps by the time windows 8 launches later this year. and people would be able to get everything they expect from a tablet on the day of the launch itself.