I don't think the time has gone to register short one word domains. They are still very much in demand more than the long keyword rich domains. Do a proper search and you will find some good one word domains still available. Short domain names are scarce, but not impossible to find. Even though one can register a domain upto 67 characters, do you think anybody would register a domain so long? Even a 23 character domain would be too long and hard to remember and type.
I consider the issue of remembrance a valid reason. What's important in online business is site's traffic, the more the traffic, the more chances of sales conversions. If you happen to register a 25 character long domain, you stand a chance to lose a certain percentage of type in traffic to your
website hosting which means a few less sales.