Noncashable Checks

I am a bank teller at a very large bank. I have noticed that some companies, Verizon, for example, as well as some insurance companies, issue checks to their customers that aren't cashable. These checks are only depositable. Our bank cashes checks for both customers and non-customers and I don't think it is fair to give someone the impression that they can cash their check, especially when they find out they can't after waiting up to 45 minutes in line.These checks look like any other check and nowhere does it say that they are for deposit only. There is no letter advising the customer of this fact either. Is there any information on this? Also, if the check is negotiable as per the 5 points of negotiability, why won't the bank cash it? Also, what is the purpose of this practice? It seems that companies that do this take advantage of people without bank accounts. An account of this type probably results in a higher percentage of "thrown-out" checks. Are these companies just greedy, or is there a reasonable explanation?