Having been a manger of anywhere from 2 to 14 employees over the years, some in retail/service at times, I cannot agree with this sentiment. Some people simply abhor any type of confrontation and I understand that, and the OP's method (which I thought was great) is more direct than some of those folks are comfortable with.

However, having found myself on both sides of the situation where managed employees were not fulfilling their assigned duties, I've always taken the attitude that if the management is not made aware of the problems then the problems are not likely to be fixed. Usually in a case such as this the area has been assigned to an employee that has gone on break or has been distracted by other duties and has failed to have someone else cover their station, or personal animosity from other employees with bad attitudes causes them to ignore covering the missing employee's area out of spite; either way - not good for business and it needed to be called to their attention.

The attitude of "it's not my job" seems to be more prevalent these days than in the past. I had it painfully explained to me early in my working career that "my job" was whatever I was asked to do (within reason) since it all paid the same, and that if I felt what I was asked to do was beneath my dignity to perform then I was free to leave and pursue other opportunities. It made me mad at the moment, but after I calmed down I had to admit the man who imparted that to me had been right - and I've carried that with me for the last 30 years.

Some may not agree with the writing of the note on the counter but simply leaving without comment is not the way to respond to the situation. I used to have some business card sized cards that I would leave on the table under a single penny that said "The Tip Would Have Been Bigger If The Service Had Been Better".