Boeing as mentioned above does hand out FCOMS that advise to deselect instead of switching it off. If only for low speed protection and G/A thrust. However they only do that if they have audited the training program of the airline in question and are satisfied with the training program.
I always wonder about that tailstrike issue, it comes up every time we discuss about this issue here. However in around 25 years operating 737s with deselecting the autothrottle we never had a tailstrike on landing. If the autothrottle is active and the (left) RA indicates less than 27ft the autothrottle will go into RETARD mode from the current TLA. That is what helped those turkish airline guys to kill themselves and a few of their passengers in Amsterdam. The autothrottle will not try to keep the MCP speed in this special case.
When leveling off it will simply try to keep the MCP speed, if the pilot isn't able to do it himself in the first place. Something that sadly seems to be a major issue in todays world of magenta line wonder boys.