Well said; I'd even take it a step further and say that your customers (unless your customers are technical folks) have absolutely no idea about the distinction anyway. Saying that it's hosted on Heroku means nothing to them.
Moreover, there may be companies hosting on Heroku who insist that the service is "white label" for any number of reasons; forcing something like onto them would devalue Heroku to those companies.
But Heroku can't know if the customer of their customers are technical folks or not and neither can you. Some people do care, the OP for example seems to care and we can assume thats because his customers do in fact care (only the OP can decide if his customers care or not).
Moreover, there may be companies hosting on Heroku who insist that the service is "white label" for any number of reasons; forcing something like onto them would devalue Heroku to those companies.