Other companies can indeed compete on hardware
right now or in the very, very near future. It's just that it will take Google and others longer to rev their software up to the same level as iOS and to get it's app ecosystem up to the same level.
Apple isn't standing still, and neither are any of the competitors. Of note,
many seem to release unfinished hardware in an effort to get into the market quickly, instead of polishing them to a high degree.
This could in turn sour users on tablet hardware.